Strange FPS drop in mission

[-Apple-Pie-]

Hello. Recently i was doing Hieracon. My FPS started at 40, then it began to drop, until it reached 16. Then, i decided to lower my graphics a bit. I pressed ESC, and you know what? FPS Rised from 16 to 50! Tested that multiple times, while menu is open, the fps is all right, but when its closed, the FPS drops severely. I though it may be FOV related, so i reduced my FOV to minimal, with no effect. Then, i was downed, tried to open menu in bleed-out, it increased FPS again, and you all know, when you open menu in bleed-out, your FOV does not change. What can it be, how can i fix my issues?

P.S. I own the new skin for polearms from Nova Deluxe Collection, cloth parts duplicated multiple times on the edge of polearm. I was using Orthos Prime.

[aerosoul1337]

Same.

Heavy FPS stuttering during Excavation missions.

My Rig is pretty good.

FPS drop from 200 to 40 sometimes.

This happens after Specter of the Rail.