Aaaand it has gone to "Please login to Bandlab Assistant to update activation status." Of course, doing as it asks doesn't help.
If it helps anyone debug, this came up after CbB crashed (dodgy plugin) having installed CbB with the Bandlab Assistant 3.0.6 a couple of weeks ago. CbB is build 13 [2018.04] x64.
I'll have to reinstall AGAIN (4th time!) to finish this project, but I think I'll have to go back to Mixbus. My internet connection isn't good enough to be downloading ~1GB every few uses.