[sciurius]

For the time being I assume the following is related.

Yesterday, during a gig, I called up a song and got the dreaded black page with the message that the song file was missing. Fortunately, I could read my partners score.

After this song we had a small pause so I ran "find missing files" and the particular file was not reported. I checked using a file manager that the file was present. Back to MSPro and lo and behold -- the song displayed normally.
This happened on the master tablet (the one that creates the backups this thread is about).

So there seem to be (transient?) situations that cause MSPro to be unable to open (read, load) a file. This may be related to MSPro making incomplete backups.