Sealed Vault crash

/sigh

So I've been saving up this map for a while, cleared stuff around, got my best juice on it and got in.
Second pack of rare mobs get hit by my spell after opening the door - have a freeze. I don't panic yet, I'm used to it - when it happens the "cogwheels of doom" appear and we're back in action, but alas - not this time!
I wait in vain only to see the game throwing me out to login screen. I log back in immidiately - the portal is gone, map counts as failed. Duhhhhh. Could be any other map, but no, ofc it's the one I need </3

What happened? Who knows /shrug
Frustration is I'm left with, but I guess it's already a meme at this point. Please make this thing more stable OR if it's not possible at least stop making em "failed" in such case, cuz the amount of prep work to get to it is the time spent and one DC due to a bug or w/e else makes it seem like a total waste.