Ideas
I've been seeing the same issue as simsllama, and I believe it started after patch 1.117.227.1030. Any time any sim, including my own, paints on an easel that is positioned outside of the boundaries of a lot the canvas stays blank. If I queue up the Scrap Painting or Put in Inventory actions the action bubble shows a preview of the painting, if I place the painting in my inventory the inventory preview image looks fine, and the painting looks completely normal when I put it on a wall, but until I take one of those actions the canvases are completely blank. All easels that are within lot boundaries and can be interacted with in Build/Buy mode, both on public and residential lots, work as expected.
So far it's been a problem on the easels at the Romance Festival, the ones in the plaza outside of the San Myshuno Art Center, and the three that are positioned in common areas around Windenburg. I just confirmed that the same thing happens in brand new saves without any mods or cc installed.
Edit: I forgot to mention, I am not seeing any errors of any kind.