[1.21.10 freeze] Client freezes when exiting World Edit screen – caused by patch activation logic (not individual patches)

[greenti-gry]

Bug Description

When Debugify is enabled on Minecraft 1.21.10, the client freezes (UI deadlock, no crash) when exiting the World Edit screen.

Singleplayer → Select World → Edit → Back

At this point:

• the screen freezes completely
• no buttons respond
• no crash report is generated
• the game must be force-closed

Although issue #505 mentions freeze/crash on buttons in world edit, my case is different — there is no exception in logs, no crash, only a UI deadlock. The issue occurs only when patches are activated; setting default_disabled: true removes the issue entirely. This suggests a bug in patch activation logic, not in specific GUI patch handlers.

(#505)

How to Reproduce?

Singleplayer → Select World → Edit → Back

Expected Behavior

Returning from Edit World should go back to the world selection screen.

Version

1.21.10+1.1 debugify-1.21.10+1.1.jar

Fabric/Quilt Loader Version

Fabric 0.18.4 for 1.21.10 (modrinth.app)

Logs or additional context

Important diagnostic results

This is NOT caused by any specific MC-xxxxx patch.

Tested and confirmed:

Disabling all GUI-related patches → freeze still occurs
Disabling lifecycle / save / tick-related patches → freeze still occurs
Disabling all individual MC-xxxxx patches manually → freeze still occurs
Removing Debugify entirely → issue disappears
Critical finding (decisive test):

Setting the following in config/debugify.json:
"default_disabled": true,

Result:
Freeze disappears completely
This shows the issue is caused by Debugify patch activation / registration logic itself, not by any single patch.

Conclusion

Debugify core / patch activation logic appears to be incompatible with Minecraft 1.21.10 GUI lifecycle
The problem occurs before or during patch activation
Individual patch bisecting is ineffective
This is a silent UI deadlock (no crash, no log error)

Notes

The issue is easy to miss because:
no crash is generated
it only occurs in a narrow UI flow
Likely a regression due to GUI/lifecycle changes in 1.21.10

Attachments

latest.log shows no errors related to the freeze
https://pastebin.com/AP7R01F9

Has not been reported.

• I made sure this bug hasn't already been reported.

Is on most update to date version.

• I made sure I am using the most up to date fabric/quilt loader and mod version.

[greenti-gry]

Update:

I have performed further testing and confirmed that the issue also occurs on a freshly created world. Even with a brand-new save, clicking the "Cancel" or "Save" button in the "Edit World" menu results in an infinite hang. This confirms the problem is not related to world data corruption or legacy files from previous game versions, but is a direct conflict between Debugify and the game's GUI/Server thread management in this environment.

[berkaygk]

Happens for me too. I disabled all the fixes from mod menu and restarted and the problem was gone, so there's probably a fix that causes this issue.

[berkaygk]

So, I figured out which fix caused the issue, it is MC-251068.

[isXander]

https://github.com/isXander/Debugify/blob/1.21.11/src/client/java/dev/isxander/debugify/client/mixins/basic/mc251068/WorldSelectionListMixin.java just putting this here for later reference

[greenti-gry]

As I mentioned earlier, in my case, the problem still occurs even after blocking all fixes completely. MC-251068 fix does not appear at all in my debugify.json configuration file. The only thing that helps with this problem is disabling the mod by setting: “default_disabled”: true.

[RatchetStuff]

Happens in 1.21.11 too. The cancel button in the world creation screen also does not work. It fixed itself, weird.