I mined the last few tiles to get to the troll in the top right corner after finishing the donut and it aggroed and I ran. Around halfway of where I'm ko'd I switched from pickaxe to b12, then ran around the corner and got insta dunked by a cave in. It was a clean 3 tile wide donut as you can see. The 1 minable tile on the left side and the 1 tile directly above my character came with the cave in.
I had 0 lag, was checking before that everything is ok, spent a few minutes checking the donut for bounding boxes and did a test run, no stockpiles nothing. Just got randomly caved in, if it's not a bug please explain since this is breaking the fight.