Strange issues with player in Musescore 4

Hi! Firstly, this score of mine is absolutely too long and cumbersome to begin with and I should probably separate it into individual files for each song. Alas, I have a score containing all of the sheet music for the musical "A New Brain" by William Finn.
On Musescore 3 (I think I was on Musescore 3.5, but I'm not entirely sure) this score was buggy and prone to crashes, but largely worked. Now with the upgrade to Musescore 4 some really strange things are happening with the playback. When started from the beginning, the player starts playing from the beginning and from somewhere around measure 2650 simultaneously. This continues up until the "second startpoint" reaches the end of the score. At that point the score plays only the music correctly and only from the right point in the score up until measure 1421, where the piano drops out al together. Seemingly, the voice lines keep going; it's only the piano that stops playing. There's also the fact that whenever you start the playback of the score, from any point, you get some kind of noise from the piano. In the beginning of the score it sounds like a slam on all the keys, but later on, when the piano has cut out, only the lowest and highest notes can be heard.
I'm linking a copy of the score if someone is interested and wants to check it out for themselves. This is in the grand scheme of things maybe not so significant a bug, as it is probably not practical or smart to have such a gigantic score to begin with, but maybe this has applications elsewhere in the programme that could prove much bigger deals in the future.

Kind Regards,
/Max