Alright after some toying, i think i figured it out.
I think the HDRI map i was using got moved or deleted, so now it's hunting for an HDRI map that doesn't exist. I tried putting a moved HDRI in another substance file from a shelf and it crashed every time. So i guess the question is how do i change the HDRI map the scene is using without opening it in painter?
I can't just replace the file because the sky i left in there was on a portable drive, and i don't remember what letter it had at the time. Nor can i just relocate it like any other missing file in a shelf
Kinda suprised there's no "hey idiot your HDRI is missing" dialogue though. Dragging and dropping something from the shelf produces the exact same result, seems like a simple fix.