Throbber Runs from simplest operation

Symphonic piece

The simplest command will prompt the throbber to run for sometimes 3 or 4 minutes before I can continue with my work.

A more recent piece does not seem to do this.

In the example attached I am merely trying to clean up rests/measures and this caused a long delay in operations.

It could be anything however that causes the delay. I can merely click on a note to modify and the throbber will run with an unreasonable delay.

My instincts tell me to re notate the entire piece from scratch (maybe 20 hours of work) but will that solve it? And is there a better way?

Any help appreciated

I am recording this piece with an orchestra on May 7 and the score is due April 6.

My score prep guy has made it look professional in Sibelius but I like to check sounds and make final alterations using Musescore Studio sounds which I noticed from the last session was fairly accurate