SOLVED Server crashed because of me (botania flower, specifically)
Marimorphosis - this flower caused the server to crash the second i placed it down and it started converting blocks. i tested on single player to the same effect.
may require a rollback to 5 mins before the crash i guess 15 mins or so before this post.
I tested on a clean client, with botania only. it's a bug in the mod and i've reported it so I would say just disable the flower for now.
disabled flower and rolled back region file