The framerate on my server seems to be unable to hold above 100 when more than 2 players join, but it’s inconsistent because sometimes it just goes to 400 and holds there for an hour no problem. CPU utilization is under 10% on a quadcore, and network bandwidth is less than 1MB / sec on 1TB connection. RAM is at a constant 7GB on a 64GB capacity. What else might be the issue here? I would have expected CPU to be maxing out before FPS drops.
This turned out to be the power options being on balanced, which apparently is a default on Windows servers.