Paintshop Pro 2020 strokes vanishing bug?

I have Paintshop Pro 2020, and whenever I switch between tools - especially paintbrush, but eraser, smudge and other tools also have this happen - particularly when I then return back to that tool, a random amount of my previous strokes just vanish. They undo themselves. Sometimes using undo or redo will repair the missing strokes, other times it only partly fixes it or has no effect.

It makes NO sense, but it also makes it basically impossible to use Paintshop Pro, because I’m constantly redoing my work over and over, and if it removes something I don’t notice, there’s no telling how long I’ll go without seeing it/I might miss a minor error entirely. It behaves very much like I’m trying to work with vectors and an anchor point is missing or something, except I’m using raster tools on raster layers. What is happening??

I talked to support, they first told me to wipe all the data and try fresh, that failed. then they said 'uninstall and reinstall', that still failed. At this point, it seems like maybe it's not even a bug but some kind of a feature that's somehow on? I use a tablet, not a mouse, it's a VEIKK tablet.