Extreme Lagging and Frequent Crashing

I have a score I've been trying to work on for a couple of week but when it is working its boredline unusable how laggy it is, but most the time a small action will cause muse score to stop responding for about 10 minutes. Things that always cause it to do this include show/hide parts.

I believe I started on a different file and tried creating a new one and copying things over (which took a long time as it had a lot of time sig, key sig and tempo changes) which helped for a bit but then it continued being like this. When I try to save it freeze for a very long time, as does closing it. Trying to open the score is very slow and now doesn't seem to be working at all.

I have tried uploading it privately to musescore but despite being uploaded it is stuck processing.
I'm not getting any file corrupt warnings or any warning at all. I tried to download the repair assist plugin, but since then the score won't open at all.

It is a wind band score, so large but not unresonably large.

Additionally, whenever there is a key signature change it doesn't seem to appear in all instruments, usually missing from parts.