Ok its getting kinda frustrating and i am not sure what might causes but before and after Server update it happend several times.
Triggering any type of Avatar event getting the Avatar to spawn , gonna get to the Avatar spawn and a bit later before you are able to engage your Avatar of your choice zone crashes.
When u log back now Avatar is gone and only option you have is run back do the whole event and hope the zone don't crash this time.
Also wich is kinda annoying are mobs that will if u dont engage em on spot vanish under the ground and only way to kill em than is either hope they summon you under the ground, use pets to kill em or use a charmed pet that is able to summon to summon em up.
Edit:
Forgot another method to handle the underground buggers :
Using levi and try find a spot floating way over the ground to force the mobs to come out.