Post Processing raw photos with the Photos Ap on my MacBook Pro sometimes ends up with the image no longer being able to be seen (becomes white/blank) when I minimize it. This does not happen with jpeg images. What could be the cause?

This seems to be a bug I am experiencing also, though I am on Catalina, not Big Sur - If it is the same problem I am seeing, not fixed in Big Sur, reverting edits to original will bring the image back to normal - after which you can edit again without problems.

The workaround I use is:

Import the raw files

Select them all (in all photos view)

CMD-E (auto enhance)

Image menu>Revert to original (while they are all still selected)

From then on they all work fine.