Everything was going wonderfully until I upgraded two machines on my network from kernel 5.7.6 to 5.7.7 .
Rolling the kernel back solved the problem. Looks like the new kernel breaks Hamachi. It runs and lists members of the network. It appears that I can login successfully but I can't connect to other machines. If I am running 5.7.6 it looks as if machines running 5.7.7 are not on the network. Looks like we'll need a new release of Hamachi to fix this unless subsequent kernel releases undo whatever problem(s) have been created.