I've figured out what is causing the unlinking of variation photos! It is by changing the price using the bulk editor. The photos are missing when changing the price using the bulk tool on your listings page, not in the listing itself. If I change the price within the listing the photos are back. So something is happening when changing prices using the bulk editor. This is why they seem to be fine for a while and become lost at different times for different people, because it is when we happen to alter prices.
I've sent a request to Etsy support so hopefully they can fix this for us!
