App crashes in function QQmlPropertyCache::property(int) const on ARM 64bit

Among others, I publish my app via Flatpak. This worked flawlessly in the past.

Recently, the Flatpak devs released an updated KDE/Qt runtime and did a pull request against my app: https://github.com/flathub/net.rpdev.OpenTodoList/pull/32

After applying the change, the x86_64 version of the app still runs fine. However, on ARM 64bit, the app crashes. Unfortunately, I currently don't have a suitable device at hand and using software emulation, I was unable to properly debug this. However, the user who reported the crash of my app to me provided a backtrace, see this comment on GitLab: https://gitlab.com/rpdev/opentodolist/-/issues/503#note_799535933

However, unfortunately, I was not able to make any sense of the backtrace. The only part of my app that is visible there is the main() function. The crashing thread is a QQmlThread (I guess, this is spawned by the QML engine), the function where the crash (a segmentation fault) happens is "QQmlPropertyCache::property(int) const".

I did a quick cross check and the only bug that could be somehow related is QTBUG-65879 (which is, however, ARM 32bit with unfortunately no solution).

Is there a way to debug this? Could additional debug output be revealed somehow?

If it helps, here's some further information from the top of my head:

• I don't think this is a general ARM 64 bit architecture thing, as the app runs fine on iOS as well as Android ARM 64bit.
• I reverted back the used Flatpak runtime of my app to the previous (working) one. However, if it helps, the beta channel is still on the new, failing runtime.
• I tried to check the Qt version used in both runtimes, however, both report as 5.15.3. Is there something (like, configuration parameters) that could influence the cache loading and hence cause the crash?

Please let me know if any additional information is needed from my side.

Thanks!