Hi Alan @asibert, after reading through your original question(s), your problem sounds very similar to one that I have recently documented and reported. Please see the document attached to this post to see if it sounds/looks like what you experienced. I documented all of the messages I get with pics of my SU session, so you can see if this is the same scenario that you are having.
Bottom line is that I have found that any time I use the Print function to save a PDF file of a model, it will cause a Failed to save error the next time I (or the Autosave feature if you are using it) try to save the model and then pop-up an error message saying that it is having an issue reaching Trimble Connect and suggesting that you Please download a backup file…but when you try to download a SKP file, it does as you suggested and hangs the SketchUp session.
I’ve never had to totally reboot my laptop to recover, as you said was necessary in your OP, just kill the SU window or tab (if you’re in a browser).
Let me know if your problem seems like the same problem I have documented, so I can refer this thread to the SU folks who are working this problem…I think it’s more widespread than they think. This is the 3rd thread I’ve linked my problem to in the last few weeks…