I might have found a probable cause for some of the server crashes.

When 2 or more are in a party and dying/joining zones rapidily at the same time the server seem to crash.

We came across this problem when we were fighting the last boss on act 3. it took us about 15-45minutes to clear the levels down to the boss. but once we reach the boss and start dying. The server seemed to crash when we'd die and zone to town at the same time repeatedly.

The server crashed 5 times when we did the exactly same thing. but the timing to reach the boss varied alot.

the variations in time to reach the same location of the boss just to crash in a similar way every time made it feel less and less like a coincidence. after thinking it over we made sure that only 1 person at a time would be in a loading screen. It took us twice as long to kill the boss but unlike before, The server did not crash.