I have discovered this twice today after many hours of painting several lines across my spaceship model to create panel lines. It will seem as though everything is working fine, but at a certain point I will realize that detail I have added will just disappear. I save often, and the lines will still be present after saving- I'm not sure when it is happening or what is causing this work to disappear. I did not reimport model at any point- it was imported when I originally created the Painter file. For the layer, I am using a fill layer with a black mask and painting the lines as white lines to the mask, rather than painting in a regular layer. My next step will be to just use a regular layer, which may or may not fix the issue. The model has a fairly large set of UDIMs (41 total). Is Painter just unable to handle that many UDIMs (sized at 4k)? Or has anyone else experienced this before and found what might be causing it?