https://github.com/front/wp-cli-build/blob/4fc75a88ff1b3561ff231aec5a5b78e21d4df152/src/Helper/Utils.php#L185 $failed_version_download is undefined, coz it was initialized in different scope.
wp-cli-build/src/Helper/Utils.php
Line 185 in 4fc75a8
$failed_version_download is undefined, coz it was initialized in different scope.