Created attachment 159571 [details]
Graphical anomaly on a new canvas

git 807c7b3

SUMMARY
For the past few months on nightly builds, I've been occasionally experiencing graphical artifacts that would appear over the canvas.

Changing layer visibility does not remove the artifacts. Removal requires either re-opening the document or changing graphics acceleration settings. 

I've attached an example that appeared on a newly-created 6071x4299 document. In this case, zooming in on the artifacts temporarily removes the artifacts, until I zoom back out.

STEPS TO REPRODUCE
1. Create large documents either through Create New File or by growing canvases through the crop tool.

OBSERVED RESULT
Occasional graphical artifacts.

EXPECTED RESULT
No graphical artifacts.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Debian Sid
KDE Plasma Version: 5.27.2
KDE Frameworks Version: 5.103.0
Qt Version: 5.15.7 (appimage)