SUMMARY
When I use KDE Wayland and switch compositor backends, the alt+tab switcher becomes graphically corrupted.

STEPS TO REPRODUCE
1. Launch KDE Plasma in Full Wayland mode (might happen in Wayland too)
2. Open Compositor settings
3. Switch rendering backend, press OK or Apply
4. Press Alt+Tab

OBSERVED RESULT
Entire left sidebar is black, except for window thumbnails.

EXPECTED RESULT
Light background, visible window text.

SOFTWARE/OS VERSIONS
Operating System: openSUSE Tumbleweed 20200421
KDE Plasma Version: 5.18.4
KDE Frameworks Version: 5.69.0
Qt Version: 5.14.1
Kernel Version: 5.6.4-1-default
OS Type: 64-bit
Processors: 4 × Intel® Core™ i5-6200U CPU @ 2.30GHz
Memory: 7.6 GiB of RAM

ADDITIONAL INFORMATION

This is a laptop. lspci output (snipped to graphics cards):

00:02.0 VGA compatible controller: Intel Corporation Skylake GT2 [HD Graphics 520] (rev 07)
01:00.0 Display controller: Advanced Micro Devices, Inc. [AMD/ATI] Sun XT [Radeon HD 8670A/8670M/8690M / R5 M330 / M430 / Radeon 520 Mobile] (rev 83)

According to glxinfo, the GPU in use is "Mesa DRI Intel(R) HD Graphics 520 (SKL GT2) (0x1916)". The AMD GPU might not be active, I don't know.

On this same machine, after opening several programs, I get an issue where Firefox turns black, and/or windows become invisible/transparent and flicker opaque when redrawn. I don't know if this issue is related.