App sometimes freezes at startup on latest master (suspected QML disk cache / Qt regression)

[noeliaSD]

On latest master, the app will occasionally hang at startup with no meaningful logs. The issue has been observed on macOS and linux, though not 100% consistently. Root cause remains unclear; evidence suggests it may be related to the QML disk cache and/or a Qt regression.

Workarounds reported:

• Upgrade to Qt 6.9.2 (may resolve)
• Delete QML cache folder (consistently resolves the issue):
  • CacheLocation : "~/Library/Caches/<APPNAME>", "/Library/Caches/<APPNAME>" , "C:/Users//AppData/Local/<APPNAME>/cache"
• Set env var: QML_DISABLE_DISK_CACHE=1

Note: First seen in PR: #18608 (review)

[noeliaSD]

It's been reproduced on 6.9.2 again randomly and really not consistently.

[anastasiyaig]

i dont know wether this issue is the reason of issues i am facing in #18724
(application is irresponsive after start). However, removing QML cache physically helped once here to get results for tests.
NOTE: the issue with the app freeze on start is also reproducible (at least for windows) with qt 6.9.2, so migration to that version did not help to mitigate the issue (or its completely different issue which is also resolvable by deleting the cache, idk)