FPS drop in arena only



I’m dropping fps in arenas. I play at capped fps on 150, but when arena starts and there isn’t anyone in stealth I drop frames to around 80 for some reason.
If there is someone in stealth, fps stays at 150 but as soon as they come out it drops again.

I’m playing on a laptop Lenovo Y530, i5 8300, 8GB ram, GTX 1050.

Anywhere else it’s fine, dungeon runs, raids, this only happens in arenas.
I’m pretty sure everything is up to date, all my drivers, windows, addons are also up to date.