Monstrous Treasure - Beyond - Multiple maps - Instance crash

I have run 2 monstrous treasures in dark forest with beyond leaguestone. Both times about halfway through the instance has crashed upon opening a strongbox. I get kicked to login screen and when I try to use a portal I get the 'failed to join any instances' message and can't go back into the map.

I rolled each map with 100+ quantity and I'm sure those detonate deads may have something to do with it too, but both times that it crashed was right after clicking a strongbox.

Is this a known issue? Are others getting this too? Maybe it's specific to dark forest? (It procced in Dark forest both times).

Ran 2 more monstrous treasures in lair of the hydra and didn't crash. Ran a forge of the phoenix and crashed after about 20 boxes.

I'm thinking not on my end because the instance becomes unavailable. Is it possible I'm crashing the instance from too many items etc?

I should also add:

I play whispering ice so there's a lot of damage spam. Also I have been running with a tempest leaguestone for IIQ so there are tempests popping around me too. My latest crash was about 5 seconds after popping the box and there were beyond monsters spawnning.