I've the same problem with my parties nearly every time.
Settings are for friends only, but within a few minutes I have a lot of stranger Sims on my lot. That's the first issue.
The second is the same like the others have: every party crashes.
Mostly it's on level 10 within minutes (12 minutes was the fastest) and it doesn't take long and I receive the Error 400 message on my screen.
I don't get the reward multiple times, like others. All my earned stars don't count and if a friend tries to rejoin my party, he gets a freeze and it looks like he has never visited it before.
If a friend tries to access the first time, they get a freeze too and one of the two possible parties per day is gone.
Throwing a party or visiting others is one of the best things in that game.
I've to admit... I'm really annoyed by the Lamazoom truck or the surprising choices, where you only get a benefit, if you pay for it.
I really don't like the Lamazoom tickets or the time it takes, until I can get another lot extension or a new room.
But here's not the place to discuss this. On the other hand... I don't think, I'm gonna play this game much longer (playing since Beta).