Created attachment 126479 [details]
System Settings with black left menus after clicking Activities

SUMMARY

I was using Plasma 5.18.2 on Wayland in a Fedora 32 KDE Plasma spin installation. I started System Settings. I selected Workspace Behaviour, and then I clicked on Activities. The two menus on the left side of System Settings became black. Clicking on the black part could still change the panel on the right to different ones, and the popups still appeared. The left menus remained black though after selecting a different screen. I'm attaching a picture of the screen with System Settings when the black menus appeared.

STEPS TO REPRODUCE
1. Boot a Fedora 32 KDE Plasma spin installation fully updated to 2020-2-28 with kwin-wayland, plasma-workspace-wayland and their dependencies installed
2. Log in to Plasma 5.18.2 on Wayland
3. Start System Settings
4. Select Workspace Behaviour
5. Click on Activities


OBSERVED RESULT
Clicking on Activities in System Settings on Plasma turned the left menus black

EXPECTED RESULT
The menu would appear normally after clicking on Activities

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Fedora 32
(available in About System)
KDE Plasma Version: 5.18.2
KDE Frameworks Version: 5.67.0
Qt Version: 5.13.2

ADDITIONAL INFORMATION

These black menus didn't occur when I selected Activities in System Settings in Plasma 5.18.2 on X. The issue appears to be specific to Wayland. The problem was present in System Settings 5.18.1 and possibly in earlier versions.