First I'm running this in Stadia.

I tried to join a multiplayer game and was quickly kicked out, I assume because the game assigned me as the main character, which I would have also been annoyed by, haha. Then I decided to just continue the campaign I had been playing solo. I logged in and started sniping off some goblins, trying to be sneaky and thin their numbers before a big fight. Suddenly I noticed that someone had joined my game, which was odd because i was set to friends only. I checked the settings and saw that it was set to anyone can see my game. I know that there are some issues with settings saving in Stadia, so I just wrote it off to that. They started running off and not listening to me asking them to stay stealthy. I kicked them off and reloaded my game, changed to friends only, and started playing... Then... The same person joined again. Now I was curious. I changed my settings to invite-only and kicked them again. Very quickly they rejoined my game. I started talking to them over VOIP again, asking how they saw my game etc, but they never responded and left a minute or two later.