When doing escalating nightmare dungeons, quite often, when I enter a new dungeon I start rubberbanding and eventually the game shows reconnecting in the top left corner and logs me out
this is more server related. The only thing u can try, if u are playing on PC, go while being in caracter selection(!) in settings and there should be somehere an option to disable joining console players. This could help. Also, this could happen by joining grps of ppl from other side of the world, which ends in high pings = rubberbanding.