Musescore 4 playback issue (instruments won't stop playing, a high note comes in and won't go away)

I just downloaded Musescore 4 and imported my composition for large ensemble. I have two problems with the playback function.

On a certain spot in the composition the orchestra plays together, then everybody stops playing but the choir.
But in Musescore4 the accordion just continues to play, even though there is nothing written for it but rests.
Also on the singer tracks there is some high pitch note, that won't go away for the rest of the composition (another 7 minutes) and gets louder. Sounds like some kind of feedback.

I isolated the part from the composition in this mscz file here "bug GitHub".

When you listen from the beginning, you see that in bar 6 there should just be the singers, but there is also a accordion chord, and also this high pitch note on all of the singer tracks. Nothing is written there.

And second:
When clicking on a note or a bar and pressing the spacebar, in musescore3 the playback would start every time. Now in musescore it sometimes won't start at all and just the blue vertical line appears and is stuck and sometimes only one instrument is playing. Selecting one bar vertically in all instruments and then playing space seems to work fine, but this is just a new small disturbance which really takes away your workflow especially when writing big scores.

I really hope somebody can help, right now I am simultaneously opening musescore 3 and 4, to allow some kind of workflow, which is not really effective obviously. I will change back to musescore 3 for the next composition, if these problems can't be fixed.

Thanks!