Problems saving a model

I’m suddenly having problems saving a model which I’ve been saving find for a week. I’m on the education web version (sketchup for schools), on a modern laptop, 32GB ram, latest version of chrome.

I’ve tried downloading the model, and that works and the model is only 270KB so not large at all.

It appears something is corrupt because when I try, for example, drawing a rectangle, it won’t complete and then I get an error “Sorry, it looks like we’re having some internal issues. Our team has been notified.”

So I’m blocked at this point. I can shut down the browser tab, reopen the model and all “appears” well but then same behaviour trying to modify and then save the model.

Is there some way to diagnose this? It seems like a waste of a week if I can’t recover this model, and without knowing why, it seems likely all models will end this way?