Having terrible FPS drops/latency spikes

[Traceless]

Hai, lately I've had this problem especially while engaging in group play. So the thing is, some time ago everything was fine. I'd play on 30-40 FPS with 100-140 ping and that was normal, I was fine with that. Lately, or, let's say since a week ago, I've noticed my FPS decrease by a tad, but day by day it's gone worse and, it legit becomes unplayable in dungeons. So let's say FPS/ping are as stated above, but once a boss is engaged, ping goes 250+ and frames drop down to like, 5. Now I don't have this problem in other games, and I play a handful of online games, so that puzzles me even more. Has anyone had this problem before and figured how to fix it? Thanks in advance.

What Naryu Sanctum looked for me the past few times. And this too.