diff --git a/src/Rules/Properties/AccessPropertiesCheck.php b/src/Rules/Properties/AccessPropertiesCheck.php
index b1e0514e8e3..ce6717addfc 100644
--- a/src/Rules/Properties/AccessPropertiesCheck.php
+++ b/src/Rules/Properties/AccessPropertiesCheck.php
@@ -140,6 +140,10 @@ private function processSingleProperty(Scope $scope, PropertyFetch $node, string
 					return [];
 				}
 
+				if ($type->getObjectClassNames() === []) {
+					return [];
+				}
+
 				$maybePropertyReflection = $this->pickProperty($scope, $type, $name);
 				if ($maybePropertyReflection !== null && $maybePropertyReflection->isDummy()->no()) {
 					return [];
diff --git a/src/Type/Php/DateIntervalFormatDynamicReturnTypeExtension.php b/src/Type/Php/DateIntervalFormatDynamicReturnTypeExtension.php
index 08f66913cc2..88306319a0a 100644
--- a/src/Type/Php/DateIntervalFormatDynamicReturnTypeExtension.php
+++ b/src/Type/Php/DateIntervalFormatDynamicReturnTypeExtension.php
@@ -7,25 +7,17 @@
 use PHPStan\Analyser\Scope;
 use PHPStan\DependencyInjection\AutowiredService;
 use PHPStan\Reflection\MethodReflection;
-use PHPStan\Type\Accessory\AccessoryLowercaseStringType;
-use PHPStan\Type\Accessory\AccessoryNonEmptyStringType;
-use PHPStan\Type\Accessory\AccessoryNonFalsyStringType;
-use PHPStan\Type\Accessory\AccessoryNumericStringType;
-use PHPStan\Type\Accessory\AccessoryUppercaseStringType;
 use PHPStan\Type\DynamicMethodReturnTypeExtension;
-use PHPStan\Type\IntersectionType;
-use PHPStan\Type\StringType;
 use PHPStan\Type\Type;
-use PHPStan\Type\TypeCombinator;
-use function count;
-use function is_numeric;
-use function strtolower;
-use function strtoupper;
 
 #[AutowiredService]
 final class DateIntervalFormatDynamicReturnTypeExtension implements DynamicMethodReturnTypeExtension
 {
 
+	public function __construct(private DateIntervalFormatReturnTypeHelper $helper)
+	{
+	}
+
 	public function getClass(): string
 	{
 		return DateInterval::class;
@@ -44,51 +36,11 @@ public function getTypeFromMethodCall(MethodReflection $methodReflection, Method
 			return null;
 		}
 
-		$arg = $scope->getType($arguments[0]->value);
-
-		$constantStrings = $arg->getConstantStrings();
-		if (count($constantStrings) === 0) {
-			if ($arg->isNonEmptyString()->yes()) {
-				return new IntersectionType([new StringType(), new AccessoryNonEmptyStringType()]);
-			}
-
-			return null;
-		}
-
-		// The worst case scenario for the non-falsy-string check is that every number is 0.
-		// `%a` format gives `(unknown)` and removes numeric and uppercase accessory but then
-		// we'll have to manually check for the non-falsy one.
-		$dateInterval = new DateInterval('P0D');
-
-		$possibleReturnTypes = [];
-		foreach ($constantStrings as $string) {
-			$formatString = $string->getValue();
-			$value = $dateInterval->format($formatString);
-
-			$accessories = [];
-			if (is_numeric($value)) {
-				$accessories[] = new AccessoryNumericStringType();
-			}
-			if ($value !== '0' && $value !== '' && $formatString !== '%a') {
-				$accessories[] = new AccessoryNonFalsyStringType();
-			} elseif ($value !== '') {
-				$accessories[] = new AccessoryNonEmptyStringType();
-			}
-			if (strtolower($value) === $value) {
-				$accessories[] = new AccessoryLowercaseStringType();
-			}
-			if (strtoupper($value) === $value) {
-				$accessories[] = new AccessoryUppercaseStringType();
-			}
-
-			if (count($accessories) === 0) {
-				return null;
-			}
-
-			$possibleReturnTypes[] = new IntersectionType([new StringType(), ...$accessories]);
-		}
-
-		return TypeCombinator::union(...$possibleReturnTypes);
+		return $this->helper->getType(
+			$scope->getType($arguments[0]->value),
+			$scope->getType($methodCall->var),
+			$scope,
+		);
 	}
 
 }
diff --git a/src/Type/Php/DateIntervalFormatFunctionReturnTypeExtension.php b/src/Type/Php/DateIntervalFormatFunctionReturnTypeExtension.php
new file mode 100644
index 00000000000..3b1de714ad5
--- /dev/null
+++ b/src/Type/Php/DateIntervalFormatFunctionReturnTypeExtension.php
@@ -0,0 +1,40 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Type\Php;
+
+use PhpParser\Node\Expr\FuncCall;
+use PHPStan\Analyser\Scope;
+use PHPStan\DependencyInjection\AutowiredService;
+use PHPStan\Reflection\FunctionReflection;
+use PHPStan\Type\DynamicFunctionReturnTypeExtension;
+use PHPStan\Type\Type;
+use function count;
+
+#[AutowiredService]
+final class DateIntervalFormatFunctionReturnTypeExtension implements DynamicFunctionReturnTypeExtension
+{
+
+	public function __construct(private DateIntervalFormatReturnTypeHelper $helper)
+	{
+	}
+
+	public function isFunctionSupported(FunctionReflection $functionReflection): bool
+	{
+		return $functionReflection->getName() === 'date_interval_format';
+	}
+
+	public function getTypeFromFunctionCall(FunctionReflection $functionReflection, FuncCall $functionCall, Scope $scope): ?Type
+	{
+		$args = $functionCall->getArgs();
+		if (count($args) < 2) {
+			return null;
+		}
+
+		return $this->helper->getType(
+			$scope->getType($args[1]->value),
+			$scope->getType($args[0]->value),
+			$scope,
+		);
+	}
+
+}
diff --git a/src/Type/Php/DateIntervalFormatReturnTypeHelper.php b/src/Type/Php/DateIntervalFormatReturnTypeHelper.php
new file mode 100644
index 00000000000..10b512d34ec
--- /dev/null
+++ b/src/Type/Php/DateIntervalFormatReturnTypeHelper.php
@@ -0,0 +1,76 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Type\Php;
+
+use DateInterval;
+use DateTime;
+use PHPStan\Analyser\Scope;
+use PHPStan\DependencyInjection\AutowiredService;
+use PHPStan\Type\Accessory\AccessoryLowercaseStringType;
+use PHPStan\Type\Accessory\AccessoryNonEmptyStringType;
+use PHPStan\Type\Accessory\AccessoryNonFalsyStringType;
+use PHPStan\Type\Accessory\AccessoryNumericStringType;
+use PHPStan\Type\Accessory\AccessoryUppercaseStringType;
+use PHPStan\Type\IntersectionType;
+use PHPStan\Type\StringType;
+use PHPStan\Type\Type;
+use PHPStan\Type\TypeCombinator;
+use function count;
+use function is_numeric;
+use function strtolower;
+use function strtoupper;
+
+#[AutowiredService]
+final class DateIntervalFormatReturnTypeHelper
+{
+
+	public function getType(Type $formatType, Type $intervalType, Scope $scope): ?Type
+	{
+		$constantStrings = $formatType->getConstantStrings();
+		if (count($constantStrings) === 0) {
+			if ($formatType->isNonEmptyString()->yes()) {
+				return new IntersectionType([new StringType(), new AccessoryNonEmptyStringType()]);
+			}
+
+			return null;
+		}
+
+		$daysIsInt = $intervalType->hasInstanceProperty('days')->yes()
+			&& $intervalType->getInstanceProperty('days', $scope)->getReadableType()->isInteger()->yes();
+
+		$dateInterval = $daysIsInt
+			? (new DateTime('2000-01-01'))->diff(new DateTime('2000-01-01'))
+			: new DateInterval('P0D');
+
+		$possibleReturnTypes = [];
+		foreach ($constantStrings as $string) {
+			$formatString = $string->getValue();
+			$value = $dateInterval->format($formatString);
+
+			$accessories = [];
+			if (is_numeric($value)) {
+				$accessories[] = new AccessoryNumericStringType();
+			}
+			if ($value !== '0' && $value !== '' && ($formatString !== '%a' || $daysIsInt)) {
+				$accessories[] = new AccessoryNonFalsyStringType();
+			} elseif ($value !== '') {
+				$accessories[] = new AccessoryNonEmptyStringType();
+			}
+			if (strtolower($value) === $value) {
+				$accessories[] = new AccessoryLowercaseStringType();
+			}
+			if (strtoupper($value) === $value) {
+				$accessories[] = new AccessoryUppercaseStringType();
+			}
+
+			if (count($accessories) === 0) {
+				return null;
+			}
+
+			$possibleReturnTypes[] = new IntersectionType([new StringType(), ...$accessories]);
+		}
+
+		return TypeCombinator::union(...$possibleReturnTypes);
+	}
+
+}
diff --git a/tests/PHPStan/Analyser/AnalyserWithCheckDynamicPropertiesTest.php b/tests/PHPStan/Analyser/AnalyserWithCheckDynamicPropertiesTest.php
index b6a160de932..5538225e419 100644
--- a/tests/PHPStan/Analyser/AnalyserWithCheckDynamicPropertiesTest.php
+++ b/tests/PHPStan/Analyser/AnalyserWithCheckDynamicPropertiesTest.php
@@ -12,9 +12,7 @@ class AnalyserWithCheckDynamicPropertiesTest extends PHPStanTestCase
 	public function testBug13529(): void
 	{
 		$errors = $this->runAnalyse(__DIR__ . '/data/bug-13529.php');
-		$this->assertCount(1, $errors);
-		$this->assertSame('Access to an undefined property object::$bar.', $errors[0]->getMessage());
-		$this->assertSame(8, $errors[0]->getLine());
+		$this->assertCount(0, $errors);
 	}
 
 	/**
diff --git a/tests/PHPStan/Analyser/nsrt/bug-1452.php b/tests/PHPStan/Analyser/nsrt/bug-1452.php
index 75e4676bddc..8e01ed8888a 100644
--- a/tests/PHPStan/Analyser/nsrt/bug-1452.php
+++ b/tests/PHPStan/Analyser/nsrt/bug-1452.php
@@ -1,12 +1,44 @@
-<?php declare(strict_types = 1);
+<?php
 
 namespace Bug1452;
 
+use DateInterval;
+use DateTime;
+use DateTimeImmutable;
+use DateTimeInterface;
 use function PHPStan\Testing\assertType;
 
-$dateInterval = (new \DateTimeImmutable('now -60 minutes'))->diff(new \DateTimeImmutable('now'));
+function doFoo(): void {
+	$dateInterval = (new DateTimeImmutable('now -60 minutes'))->diff(new DateTimeImmutable('now'));
+	assertType('lowercase-string&non-empty-string&numeric-string&uppercase-string', $dateInterval->format('%a'));
+	assertType('float|int', $dateInterval->format('%a') * 60);
+}
 
-assertType(
-    'lowercase-string&non-empty-string',
-    $dateInterval->format('%a')
-);
+function doBar(DateTime $a, DateTime $b): void {
+	$interval = $a->diff($b);
+	assertType('lowercase-string&non-empty-string&numeric-string&uppercase-string', $interval->format('%a'));
+	assertType('lowercase-string&non-falsy-string&numeric-string&uppercase-string', $interval->format('%R%a'));
+}
+
+function doBaz(DateTimeInterface $a, DateTimeInterface $b): void {
+	$interval = $a->diff($b);
+	assertType('lowercase-string&non-empty-string&numeric-string&uppercase-string', $interval->format('%a'));
+}
+
+function doDateDiff(DateTime $a, DateTime $b): void {
+	$interval = date_diff($a, $b);
+	assertType('lowercase-string&non-empty-string&numeric-string&uppercase-string', $interval->format('%a'));
+}
+
+function doPlainInterval(DateInterval $interval): void {
+	assertType('lowercase-string&non-empty-string', $interval->format('%a'));
+}
+
+function doDateIntervalFormat(DateTime $a, DateTime $b): void {
+	$interval = date_diff($a, $b);
+	assertType('lowercase-string&non-empty-string&numeric-string&uppercase-string', date_interval_format($interval, '%a'));
+}
+
+function doDateIntervalFormatPlain(DateInterval $interval): void {
+	assertType('lowercase-string&non-empty-string', date_interval_format($interval, '%a'));
+}
diff --git a/tests/PHPStan/Rules/Operators/InvalidBinaryOperationRuleTest.php b/tests/PHPStan/Rules/Operators/InvalidBinaryOperationRuleTest.php
index ea25383fde3..771080edd3b 100644
--- a/tests/PHPStan/Rules/Operators/InvalidBinaryOperationRuleTest.php
+++ b/tests/PHPStan/Rules/Operators/InvalidBinaryOperationRuleTest.php
@@ -853,4 +853,9 @@ public function testBug10349(): void
 		]);
 	}
 
+	public function testBug1452(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-1452.php'], []);
+	}
+
 }
diff --git a/tests/PHPStan/Rules/Operators/data/bug-1452.php b/tests/PHPStan/Rules/Operators/data/bug-1452.php
new file mode 100644
index 00000000000..283c988ac9c
--- /dev/null
+++ b/tests/PHPStan/Rules/Operators/data/bug-1452.php
@@ -0,0 +1,10 @@
+<?php
+
+namespace BugRuleTest1452;
+
+use DateTimeImmutable;
+
+function doFoo(): void {
+	$dateInterval = (new DateTimeImmutable('now -60 minutes'))->diff(new DateTimeImmutable('now'));
+	$minutes = $dateInterval->format('%a') * 60;
+}
diff --git a/tests/PHPStan/Rules/Properties/AccessPropertiesRuleTest.php b/tests/PHPStan/Rules/Properties/AccessPropertiesRuleTest.php
index eeda2fb9222..dd60c3f9d48 100644
--- a/tests/PHPStan/Rules/Properties/AccessPropertiesRuleTest.php
+++ b/tests/PHPStan/Rules/Properties/AccessPropertiesRuleTest.php
@@ -1272,4 +1272,26 @@ public function testBug13537(): void
 		$this->analyse([__DIR__ . '/data/bug-13537.php'], $errors);
 	}
 
+	public function testBug12390(): void
+	{
+		$this->checkThisOnly = false;
+		$this->checkUnionTypes = true;
+		$this->checkDynamicProperties = true;
+		$this->analyse([__DIR__ . '/data/bug-12390.php'], []);
+	}
+
+	public function testBug13539(): void
+	{
+		$this->checkThisOnly = false;
+		$this->checkUnionTypes = true;
+		$this->checkDynamicProperties = true;
+		$this->analyse([__DIR__ . '/data/bug-13539.php'], [
+			[
+				'Access to an undefined property object::$baz.',
+				29,
+				'Learn more: <fg=cyan>https://phpstan.org/blog/solving-phpstan-access-to-undefined-property</>',
+			],
+		]);
+	}
+
 }
diff --git a/tests/PHPStan/Rules/Properties/data/bug-12390.php b/tests/PHPStan/Rules/Properties/data/bug-12390.php
new file mode 100644
index 00000000000..fd4ba67afda
--- /dev/null
+++ b/tests/PHPStan/Rules/Properties/data/bug-12390.php
@@ -0,0 +1,22 @@
+<?php
+
+function testIssetOnGenericObject(object $obj): void
+{
+	if (isset($obj->foo)) {
+	}
+}
+
+function testChainedIssetOnGenericObject(object $obj): void
+{
+	if (isset($obj->foo) && isset($obj->bar)) {
+	}
+}
+
+function testIssetAfterIsObjectNarrowing(string $date): void
+{
+	if (is_object($obj = json_decode($date))) {
+		if (isset($obj->crashId) && is_string($obj->crashId)) {
+			var_dump($obj->crashId);
+		}
+	}
+}
diff --git a/tests/PHPStan/Rules/Properties/data/bug-13539.php b/tests/PHPStan/Rules/Properties/data/bug-13539.php
new file mode 100644
index 00000000000..845c927a48c
--- /dev/null
+++ b/tests/PHPStan/Rules/Properties/data/bug-13539.php
@@ -0,0 +1,31 @@
+<?php
+
+function broken(string $x): void {
+	$tmp = json_decode($x, false);
+	if (!isset($tmp->foo) || !isset($tmp->bar)) {
+	}
+}
+
+function works(string $x): void {
+	$tmp = json_decode($x, false);
+	if (!isset($tmp->foo, $tmp->bar)) {
+	}
+}
+
+function works_too(string $x): void {
+	/** @var stdClass $tmp */
+	$tmp = json_decode($x, false);
+	if (!isset($tmp->foo) || !isset($tmp->bar)) {
+	}
+}
+
+/**
+ * @param mixed $tmp
+ */
+function also_ok($tmp): void {
+	if (isset($tmp->foo) && isset($tmp->bar)) {
+		echo $tmp->foo;
+		echo $tmp->bar;
+		echo $tmp->baz; // intentional: baz not checked by isset
+	}
+}