Through the process of trial and error, I have found that if when it "crashes" I disconnect the thunderbolt ethernet adapter, the system unfreezes and comes good. I can then plug it back it, although the network manager doesn't seem to notice ethernet is back again.

 

Furthermore, if the ethernet adapter isn't plugged in, it doesn't freeze in the first place.

 

Weird.

 

At least now I have a good workaround... Fingers crossed.