I've completed the pre-requisite quest in Wolfskull cave, and returned for the reward. That quest is now showing completed. I've left Solitude and leveled up several times (20 to 25) and "sqv MS06" still shows it's Stopped, with stage=0 - i.e. it hasn't been started. The Story Manager logs are not helpful, and do not contain "MS06', so it doesn't seem to be a failure to fill aliases.

I read somewhere that the Unofficial Patch changes the trigger from a Level-up to a Location change, but that should still show in the SM log.

I saved, tried "starquest MS06" and checked again, still at 0, stopped, which looks like an alias failure, but in that case something else would have to be blocking it, to prevent the SM from trying it, and showing the failure in the log.

Any clues?