Server Help Major performance issues on modded dedicated server running on quad core CPU

I'm running the dedicated server software on a Windows Server 2008 R2 server with an AMD Athalon II X4 630 CPU and 8GB of RAM. I'd expect that to be plenty to run a dedicated server for a 2D game. I know that world generation takes up a lot of CPU, but this thing used to run a Minecraft server effortlessly. It also ran a heavily modded Starbound server back in 2016 without any lag. I know it's nothing to do with any of our Internet connections as I'm connected over 1Gbps LAN and still experience problems.

For some reason both everyone's client AND the server lagspike/freeze frequently. The CPU usage I've noticed is really high. It also seems rather single-threaded; One core is on average ~90% usage while the others average about ~20%. The biggest contributor seems to be when people teleport. If someone teleports to me both my client and the server freeze for a few seconds. When my friend teleports between his ship, the world we're on and the outpost the server freezes and I can't open doors or crates for a moment. The server also freezes occasionally when no one's teleporting. At first I figured the issue was loading worlds off of the hard drive so I put the storage directory on a RAM disk but it's done nothing for performance. I finally decided to write this post after one friend started getting kicked "due to inactivity" every time he tried to teleport to me and my other friend and eventually all 3 of us simutaneously got kicked. We've had the "kicked due to inactivity" before as well. Another problem I have, but I'm not 100% sure everyone on the server gets, is extremely long loading times with almost zero hard drive activity.

Here's a link to my log file from starting up the server which includes all the mods: https://pastebin.com/dZyEPseN

 

So, I noticed that my client is also using 100% of one core. In fact I noticed this on the main menu of all things. So I assumed either one of the mods is broken or possibly even has a bitcoin miner slipped in by a malicious mod author. I unsubscribed from all workshop mods and reinstalled the game and it still eats up nearly 100% of one core on my i7 2600s at the main menu. The weird thing is a few times I started it up and it only took about 5% of the entire CPU, which is somewhat reasonable for the background animation. Not sure if this is some kind of bug or something's wrong with my system. I can't see the game being that unoptimized that it eats up an entire core of an i7 on the main menu.