it's hard to be sure, of course the apps only crash when I don't want them to ;-)
It looks like the crash only happens when linked via dropbox and perhaps only when open on ios/macos at the same time. I was editing only on one device at the time, of course.
I had this situation when a page kept switching back to an older state, many times. So this might be related to some other bug I've read about, that pages are marked as changed, as soon as document is opened. Maybe the one just open was saving itself all the time, overwriting the newer version...?
As for the upgrade message, you can provoke that by simply removing the storeinfo.plist file. One of the files that went missing on the crashes.
Yes, I was able to recover from backup. But it's only useful with syncing for me and I don't feel comfortable with depending on it as it is now. So I exported my data to some other app, again :(