Saving new or old project WITH MASKS does nothing

For several photo sets, once I add masks (created by exporting them from said project), everything runs normally (e.g., model creation, model coloring, texture creation, detecting markers), but the project will not save.

If I choose any method for saving, the overlay shows up and counts up the time. The progress bar does nothing. CPU and network use are at 0%.

I’ve waited an entire night for one project - nothing!

This is not a network or HDD issue; other projects are fine.
As long as I do not add masks, everything is fine.

Any ideas?