Britechester Home Invasions?

@Braxien Yes, I have this same thing occasionally happen in a Foxbury uni housing lot that I converted into residential so my Sim could live there permanently. It's almost like the game takes a second or two after a loading screen (travel or CAS) to recognize it as a "residential" lot and just for an instant it will spawn NPC townie university students as living in the University Housing lot. I haven't yet figured out how to prevent it but the townies usually leave right away or I can shoo them out fairly easily.

I'm getting a few of the non-loading screen uninvited visits from townies as well. One time during a soccer game event I had a streaker run in the back door and straight out the front. I also get bots from the Bot Savant events just come into my house but they are A LOT more welcome than the streaker was! xD

@Braxien I don't think what you are seeing is uncommon for Britechester lots that have been converted from Uni Housing to Residential. The game seems reluctant to treat these residential lots the same way it does for lots in other worlds. I'm not 100% sure but it seems like most of my uninvited guests are part of some event occurring on campus, like student organization events, sports events, etc. The bots from the Bot Savant events will sometimes stay at my Sim's house for days at a time. That's the Foxbury campus though so it would be different than what you are seeing at UBrite.

As far as invited guests not seeming to want to leave, yeah I have seen that too. My young adult Sim's mom shows up for visits several times a week and sometimes stays until well after midnight until I banish her with MCCC mod commands ;-D The mom is an NPC since my Sim moved out of the family home to start Uni. I've never just let it play out to see how long she'd stay otherwise but I might try it the next time I play that save. 

@Braxien In my mind my Sim feels like part of the faculty at Foxbury and that the house she is living in is more like faculty housing rather than a private residence. I've even kept the outside appearance the same (except for adding a garden) to go along with this story-line I have created entirely in my head. She's a full-time Botanist working on a second degree in Psychology and when she finishes that I will switch her over to being a professor. If I was playing any other story-line I don't think I would choose to live in Foxbury. I can put up with a certain amount of Uni student foolishness as just being part of what a faculty member might have to put up with in a Sims world, but if it gets to be too much I will just move her somewhere quieter.

Coincidentally, this Sim won The Lottery (1 million Simoleons) while she was still a full-time student so she can pretty much live anywhere she wishes ;-D

@Braxien Currently a bug report related to uninvited Sims wandering around your house is active in the bug forums. As you've converted university housing to residential, your issue could be a little different. Can you please open a new bug report about this on the bug forums.