I just tried to open a few older projects. The projects opened as blank and were subsequently deleted by the app (They were not blank). I opened a few more and they opened as expected.
I’ve a backup saved of all my projects so I’m going to try restoring this evening, look at the project json to see if anything’s odd, and see if the same projects get deleted again.
I have an iPad Air with iOS 10.2. I also have the 2nd Beta version that came out for 3.21.0, but don’t know if this is specifically associated with only the latest Beta. Just wanted to give a heads up. I’ll advise of anything I figure out this evening.