Huge FPS drop at all bosses (instance only)

[Seria]

Only happens when I get up close to a boss in an instance, not a wb. If I back away from him my fps goes back up. It doesn't matter if I am in a solo dungeon or party dungeon with ctrl+F on. I know it's not me, my rig is good (win 10) with an i7 5960x and two r90 290x. I've tried with graphics at the lowest and still it occurs. Other things I've tried includes disabling all services including razer, checking for unparked cores, overclocking. Only thing I haven't tried is downgrading from the crimson drivers.. If anyone has experienced this weirdness or has any advice please let me know, I can't seem to figure it out, initially thought it was the effects but it wasn't. Have tried turning off all interface features too. 

[Shagato]

Same problem here. During normal gameplay, my fps are basically fixed at 60 fps. Even if a whole group goes haywire on a single mob, no drops beyond 40 fps I think. But as soon as it is a dungeon boss and I stand next to him in a fight, my fps drops below 20. If I move back just a few steps, it goes up to 40-60 (my cap due to monitor). If I go into melee again, it drops again.

 

Speccs: I7 4770k, R9 290, 24gb Ram.

 

Since you also have an AMD-GPU, maybe that's a problem with that. My buddy (exactly same PC) also has this problem, while I know a few people who have Nvidia GPUs and report no such fps-drops.