I've tried to replicate the bug a few times, but haven't been able to find any pattern apart from me being already logged in.
If I'm logged in, close the site and later on open the site in a new tab or window (chrome or firefox both do this) then I sometimes see another account from my own logged in. It is never the same account, and the occurence is otherwise random.
I have not experienced this on mobile yet.

Feedback isn't around anymore, so I didn't know where else to post this.