Server lag and low FPS

Hi

My Rust server has problems with really low fps which result in lag. Problem comes around ~180 players and performance and then increases. I had the issue for some monthst now, but 4-5 months ago server had 300 players online and no issues at all. I now performance in Rust degrades over time, but this is insane. The fps it not insanely low all the time just now, the server has 200 players online and FPS is 30-40, but sometimes drop.

Server has:
Intel Xeon Gold 6144 3,5GHz CPU, 4 cores
12 Gb RAM
NVMe SSD disk.
Windows Server 2016 Standard

It's running on HyperV.

It's running a few Oxide plugins, but only for admin purposes. It's a vanilla server. Problem exist without Oxide too.

Performance monitor:
https://imgur.com/a/HdsSnZm

Disk:
https://imgur.com/a/1E1ULGE

Console:
https://imgur.com/3Uov2W6 

I would appreciate any help or pointers. Really hope someone can help.