[Bug] Startup hang on Mojang screen with HMCL, works with PCL2

[MCForgeTitle123]

• I have checked the issues and FAQ and confirmed that this problem has never been submitted before.

Describe the bug
The modpack hangs indefinitely on the Mojang screen after the loading bar completes when launched with HMCL or other launchers. However, it can be launched successfully with PCL2.

To Reproduce

1. Install the modpack 1.21.11-v10-2.9 version.
2. Launch it using HMCL with Java 21.
3. Observe the game hangs after the loading bar finishes.

Expected behavior
The game should launch successfully and proceed to the main menu.

Screenshots/Logs
[Attach your log file here]

Additional context

• The mru resource pack is corrupted, causing MalformedJsonException errors in the log.
• Multiple optimization mods (C2ME, ModernFix, VMP) are loaded simultaneously, which may cause conflicts.
• Some resource packs (e.g., font packs, glowing ores) have incompatible pack_format versions for 1.21.11.
• The issue seems to be related to Java 21 compatibility, as PCL2 uses Java 17 by default.

[EndlessPixel]

Please provide Logs File to help troubleshoot the problem

[MCForgeTitle123]

Here are the latest.log and debug.log files when the game hangs on the Mojang screen. The key error is "MalformedJsonException" of the mru resource pack, and there are conflicts between optimization mods (C2ME + ModernFix + VMP).

minecraft-exported-logs-2026-02-27T10-03-24.log

debug.log

latest.log

[EndlessPixel]

I checked your log file and found that you have successfully started it
[10:10:47] [Render thread/WARN]: Game took 39.501 seconds to start
It just took a long time, which is not a problem. This does not match your report, and you are using PCL2 to launch Minecraft, not HMCL.

[MCForgeTitle123]

Sorry for uploading the wrong log before! The following is the log of the game hanging on the Mojang screen when launched with HMCL (Java 21), while PCL2 (Java 17) can start but takes a long time. The core difference is the Java version and loading logic of the launcher:

minecraft-exported-logs-2026-02-27T10-40-51.log
minecraft-exported-jstack-dump-2026-02-27T10-40-55.log
debug.log
latest.log

[EndlessPixel]

I took a rough look, and the minecraft-exported-logs-2026-02-27T10-40-51.log you uploaded is exactly the same as the latest.log, so there’s no need to upload it again.

[EndlessPixel]

I checked the minecraft-exported-logs-2026-02-27T10-40-51.log you uploaded and found that it is a deadlock issue with the Litematica mod.

Nature of the Problem:
The projection manager thread of the Litematica mod experiences deadlock/live lock:

• Three Placement Manager threads continuously occupy the CPU (for 40 seconds).
• Thread 1 is blocked, waiting for a lock held by Thread 3.
• Threads 2 and 3 loop between getNextTask and run, creating a live lock.

You didn't encounter this issue when launching the game with PCL2, so we speculate that it might be a Java issue or an HMCL issue.