many problems with 3.O new musescore in Mac Os,
S3 - Major
there's many problems, as changing duration in a bar (occult), the program hanging suddenly, no saving changes at all, buff,
too many hours lost
the same computer has no any problem with 2.0 version
In order to understand and assist, we would need you to attach the score you are having trouble with and give precise step by instructions to reproduce the problem. If you have more than one problem to report, please use separate threads. Or, perhaps better, ask for help in the Support forum first so we can see what are actual bugs versus just things that have changed.
You mention changes not being saved, that's certainly not the case, most likely you are just looking in the wrong folder for your files. Again, asking for help in the Support forum would be a good idea.