game crashes upon joining instance with someone

Since act5 (done yesterday so maybe 3.1b has something to do with it) i have experienced relentless crashed when joining instance with my buddy in it.

It was very clear during boss teamfights: everytime i'd tp back to refill flasks (taking my tp or his) the game crashed.
So we tested out:
- my buddy would go to a zone and i would try to join him, game crashes. I tp forth and back from a zone with him in it game crashes.
Even crashed during lab.
- we both removed all of our mtxs. since then the crash is more random, it only happens sometime, 2 out of four on kitava.


It is very frustating because it means i can only kill or die trying, every time i try to escape or refill it crashes and then i may miss the boss kill and need to do it again. During labyrinth it is utterly unpleasant.
For the moment it means if i want to play with someone i need to remove all mtxs and be sure to always open zones and be tanky enough for not having to refill my potions during fights.

I'll try to link log file next time it crashes.

Who is the party leader when it crashes? My friend and I are having the same issue and we've noticed only the party leader crashes when changing instances; the other person is just fine.

same problem here when i die and trying to join boss fights again...

cant proceed the game...omg fix it...i can not kill the boss at act5...i crash when i join the instance...Any admin can answer here fast?dont know what to do...Happens every time i join boss fight at act V karuim fortress!!!!