ZBrushCentral

BPR render issue

Render issue
I’m having a bit of trouble with BPR rendering, see the (cropped) image. The rendering is striped vertically. In this project, the renders were OK for a while but suddenly I got those lines. I tried to revert the rendering and light settings but apparently the stripes are there in any setting now. Test render in another project renders fine without the stripes.
Have I accidentally triggered some unwanted setting myself while experimenting with BPR? Graphics card issue (if so, why other project is fine)? How can I further debug?

ZBCore 2020.1.3

EDIT: I got some clean renders now… if I zoom close, the render is fine. Then I can zoom out somewhat and still get a nice render. In some point (after zooming, rotating, panning) it get stripes again. Moving a little bit can help, but sometimes I have to start with close-up again to get clean renders. I tried to reduce polygons (original has about 9 M) but I still had to do the zoom-trick to get it render clean. Maybe my oldish PC just can’t handle the project very well.