Section Tool crashes SU

The section creation tool crashes SU just after cutting a section. This seems to be a corruption of my model that occurred just after 17 April 2021. I’ve gone to backups and opened the 17 April model and the section tool works fine. Nothing else appears affected, including the sections created prior to 17 April. My model has grown from 8MB then to 103MB now, so I can’t go back to the 17 April model. I’ve purged unused, and that didn’t help. When I attempt to take a section, the tool cuts it and then the donut spins forever. If I touch any other command, the screen greys. The only way out is to abort SU and restart. I’ve also tried other models, and the section tool operates perfectly. This problem is unique to this model. I don’t think this is related to file size; my backup model from 18 April has the same size and has the same problem. Assistance will be greatly appreciated, thank you! I’ve attached a screen image, if it doesn’t appear properly please let me know and I’ll redo - I’m new here.

Try this:
Activate the section tool, hit Alt + Spacebar, than ‘m’ and an arrow key.
Move mouse.

I tried several combinations of Alt+Spacebar, then m and an arrow key. No luck, as soon as i touch the arrow key the doughnut starts to spin and the screen greys.

Are you using 2 monitors?

The Alt + Spacebar is universal in Windows, the ‘m’ might be different in other languages (it’s ‘r’ in Dutch)

Open another program, then hit Alt + Spacebar, you get to see what you should tick next.

Than hit an arrow key and move your mouse.