The printer should have a cover on it for UV protection if nothing else while in use, right? So if anything you're drawing air around the printer but not really over the vat and plate

This would be my guess as well. There's adjustment possible where the little wheels in the track meet up with the door sections, if it's dragging against the frame too tightly. You want a reasonably tight fit for low airflow, especially if you've paid more for insulated door, but if you're just "scraping' it along the garage framing either side it might be sensing the added friction in some temperature and humidity conditions (depends what your framing is) and that's what's making it stop and reverse vs. fighting it.