SUMMARY
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STEPS TO REPRODUCE
1. Open affected software (Renoise in this case)
2. Use for at least 10 minutes, saving modules frequently. Less time is needed if any Electron wrapper application is running (for some reason?)
3. Attempt to input notes on the tracker matrix

OBSERVED RESULT
One keypress is registered, then keyboard focus is deflected away from Renoise. No idea where it goes. Clicking re-latches it. Renoise does not indicate that the focus has gone elsewhere in Renoise.

EXPECTED RESULT
Keyboard focus remains persistent on Renoise, allowing the software to be used.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: Devuan GNU/Linux (also observed in Arch Linux and Debian Stable)
(available in About System)
KDE Plasma Version: 5.27.2 (observed as old as 5.7, untested prior)
KDE Frameworks Version: 
Qt Version: 5

ADDITIONAL INFORMATION

Observed consistently in KWin wayland sessions for the majority of the history of the history of KWin as a wayland compositor, when using Renoise. Previously seen in Ferdi as well, seems to have been fixed their-end as of the fork to Ferdium. Issue does not present in KWin X11 sessions, nor any other wayland compositor (ruling out a Renoise issue). Issue has been final blocking item to using Plasma in Wayland for multiple years for myself and I had wrongly assumed that it would have already been reported.

Bug is more likely to happen quickly if the session has been running for at least four hours, but is always a "matter-of-time" subject, and not a "will-it-happen" subject. Longest I have been able to continually use Renoise for in a Plasma 5 wayland session was 25 minutes, directly after boot and going straight into Renoise. Shortest was 10 seconds, 5 days after boot.

If relevant, this has been observed using locally-built from-git mesa on AMD graphics hardware using the amdgpu and radeonsi driver set. This has not been tested with distro mesa on debian or devuan, but was present with distro mesa on arch linux. This has been tested with only one keyboard, which presents one keyboard, two mice, and one controller device, to the operating system. These are mentioned due to feasibility that this bug may be of the "distant ramifications" sort.