I held back upgrading from Cubase Pro 10.5 to Pro 11, due to the problems reported by others.
But today I took the plunge and it went very smoothly.
I did make sure to first perform the eLicenser Maintenance Tasks, and to update Steinberg Download Assistant.
The only minor glitch was that all of my first attempts to install the optional content packs failed. No big deal; my second attempts were successful.
I guess I shouldn’t say “painless”, because I did have to pay for the upgrade, LOL. But I’m not complaining…it’s very much worth it.
YMMV, but it worked for me.