My apologies for the long overdue response. Your messages to muse-support were temporarily misplaced as an unintended side effect of changes to the e-mail routing system. I now have those messages.
We have a theory for what may be causing the hangs on open. Please try the following at let us know the results.
Disconnect for your network.
Attempt to open one of the problem files.
Did it open successfully?
Depending on the result, I'll provide next steps. Thanks.