Score and parts not syncing properly

I'm having some major issues with the syncing between parts and score. In particular, the rehearsal letters and text objects remain as before in the parts when deleted from or changed in the score. I'm writing a piece for marching band in Musescore 4.2 and this problem has taken a LOT of unnecessary time, because the only way to fix it is to go into every single part and change it manually. This happens every time I remove rehearsal letters or text, and it has happened with ties and slurs as well. The piccolo part for example was once completely empty of slurs even though they were in the piccolo in the full orchestra score. I had to manually add them in.

See the example below. The full score screenshot only shows letter A, but it is correct according to where I want the letters to be placed. The abomination in the parts was the result of editing rehearsal letters in the score. Before the changes were made in the score below: A was in the beginning, B was were the second A now is, C was were the second B was, D was where it still is, E was were the second D now is, and so on.

To

If anything is unclear, please ask away. I tried to be as clear as possible but it's a bit complicated. I'd be really thankful if anybody could help me, or at least relate to this issue!

Edit: replaced screenshots with the entire score+parts instead.