This has been happening a lot lately to me. I'll Join a party and show up in Moorcroft. After heading towards the elevator the screen will fade to black and the haven load screen will come back up. I've had it happen multiple times in a row. I see this as a huge issue as it cuts people out of getting into T2 if they get stuck in the loop as I have.
Moorcroft manor randomly sends you back to haven
Same problem, happens every time I join a random party that's at Moorcroft.
If you get kicked by the leader it shouldn't send you to haven, but rather you would be in moorcroft manor solo (unless others join party). The issue here is that the system will take your 200 crowns even if attempting to start a tier 2 run has you going to haven instead of a tier 2 depth.
I usually keep my party locked and solo farm. Also, I usually wait near the elevator for floors to change or do a check to see if I have the right gear for the floors below. I was booted 3 times from Moorcroft back up to the arcade after being there less than a minute. Lost 600 crowns. Since I still needed to farm, on the 4th trip down, as soon as I materialized in Moorcroft, I made a wild dash to the elevator and made it down without getting booted.
Does it happens when you create the party? Maybe party leaders are kicking you. I hate when they leave party open and then do that.