Musescore 4 not saving slurs and mixer is confused

Why does Musescore 4 not save slurs? There were many in this score, but after saving and reopening it, they are all gone.

Why does Musescore 4 not include VIolins I in its mixer? Instead there are two entries for Violins II. In the second movement, I change instruments in both Violin I and Violin II to solo players, then a few bars later change back to section acoustic. Could this have confused the confuse the mixer? How can I resptore Violin I into the mixer? Musescore says my software is completely up to date. Thanks for any help.