One thing I would try is to use 127.0.0.1 instead of localhost in the command, because localhost is just a name that can resolve to whatever address on the server:
ssh -L 5901:127.0.0.1:5901 chrismuller@andreas
That worked, thank you Levente!
I logged in and checked the processes, there were no stuck Mutex's as we've gotten a few times in the past.
So it's looking more and more like it was probably just that background indexing that was happening at that moment. My guess is, response times are reasonable again.