help, framerate tanks ONLY on fortuna

[Soy77]

orb vallis might stutter a bit when i first enter, textures might load a little slow at first. but after a couple of seconds the problem usually go away, i can do bounties or other stuff like usual there.
but when i go back to enter fortuna, framerate will drop to like 5 frames per second, barely able to move.

necralisk is fine, cambion drift is fine. i can go back and forth no problem.
cetus is fine, plains of eidolon is fine.

i have tried various combinations that might trigger it, multiple times. the problem seems to consistently appear when i enter fortuna from orb vallis. other than that, the whole game is running smoothly

 

any ideas what can i do to fix it?

thanks in advance