Diamora, Song of Death despawning during fight

The Act 4 Boss on one of the Karui archipelago islands has despawned on my friend and me 3 times in a row during the time where the servers were having issues(since we were both lagging no matter who owned the instance)on the 15th of september between 21:30 and 22:15 CEST.

The boss had a chance to disappear any time she went underwater after the siren song attack with the adwaves. I'm not sure if it is caused by multiplayer(between someone from europe and america) or the server having troubles.

PS: I just realized I posted it into the PoE 1 forum, my bad, I'm sorry.