Score is responding slowly,
Unknown - this began to happen after the program hung when I was doing a copy and paste
The score responds slowly to simple instructions like highlighting text and deleting it, or copying lyrics.
Also slow was save and export. After waiting several seconds for export to respond, I exported to musicxml, and the resulting file would not load. I changed its name to .xml and loaded it fine with musescore 2.
Then I saved the file as mscz from musescore 2 and opened it with version 3 and all seems fine again.