I’ve seen it a while and hoped it would go away with the current Ventura beta, but it sticks:
When I open DPL (and it starts in Library view), the thumbnail/frames are just a little bit too big. See how the scroll handle overlaps the frames:
When I wiggle the thumbnail size slider a little bit, size will adjust as expected and the handle will be inside the scrollbar…but DPL falls back to the slightly oversized thumbnails when it is restarted.