SUMMARY
I use the Global Menu applet and am seeing problems with LyX (version 2.3.6.1), which is a document processing program that uses Qt for its UI. Upon launching LyX, the menu works fine. However, after working in LyX for a while, the menu stops working, submenus cease to appear.

STEPS TO REPRODUCE
1. Start LyX.
2. Work in LyX for a while, opening/closing menus and so on.

OBSERVED RESULT
After a while, menus stop opening: the top-level menu item in the manu bar is highlighted, but no submenu opens.

EXPECTED RESULT
Submenus should open every time.

SOFTWARE/OS VERSIONS
Operating System: openSUSE Tumbleweed 20211027
KDE Plasma Version: 5.23.1
KDE Frameworks Version: 5.87.0
Qt Version: 5.15.2
Kernel Version: 5.14.14-1-default (64-bit)
Graphics Platform: X11
Processors: 8 × Intel® Core™ i7-8550U CPU @ 1.80GHz
Memory: 15.5 GiB of RAM
Graphics Processor: Mesa Intel® UHD Graphics 620

LyX version 2.3.6.1 from the OpenSUSE repositories.

ADDITIONAL INFORMATION
I've reported this on the LyX bugtracker: https://lyx.org/trac/ticket/12415
The developer there says that LyX is generating the menus on the fly when you enter the top-level menu, it's their way of adjusting the changing menu contents. The developer uses global menus with Unity and says it took them a while to get right back at the time (4-5 years ago). It may be an issue between the way KDE displays the menu and the way LyX generates them, but for me it's a bit hard to track down.

There were some issues with this with KDE in the past (#399975); this issue is different because it only appears after a while.