Looks like a bug to me. It will be hard to figure out which file it is, maybe there could be some clue in Help > View Error / Debug log.
If this is a specific file and you can find that file and reproduce the issue we probably could fix this. But I suspect it might be some issue happening rather randomly, in which case this will likely be very hard to debug and fix
If you try to load the files again and this does not happen again I think you should not worry too much about it for your usage. But if it happens every time or at least often when you load the files please let us know, best with all the output you see in the error / debug log.