Thanks Rusty.

I should have mentioned, that’s actually exactly what I tried. I saved a few new versions of the project, then when I noticed the banks were unavailable I tried both copying the bank files manually on my computer and using the OT file manager utility. I guess it’s worth mentioning that when I looked at the project on my computer, the .strd files were missing for those banks. After I copied them, the project acted the same way when I loaded it again.

And the banks in question were (as far as I can remember) blank, so I’m not worried about recovering them so much as solving the mystery. Also I’d rather it didn’t start happening to other banks I do have stuff in.