High CPU Useage While Playing and Streaming

Hello, been trying to figure this one out. originally I thought this was an issue with OBS but I noticed if I stop streaming and just try and watching a youtube video or a stream on twitch the CPU utilization for Core 0 goes to 100% and chokes out the video stream. It gets really choppy or stops playing altogether, This only happens when I have FFXIV as the focused window. If I select the browser it runs fine. I noticed in resource monitor that when the game is focused, core 0 jumps up to 100% It doesn't matter which browser I use either, chrome or firefox, I get high CPU usage.

framerate in the game stays fine though, no stuttering or dropped frame (average framerate is 60fps at maximum) I tried lowering the quality settings but the performance issues are unchanged.

Does anyone know what could be causing this? Everything worked fine up until sunday. I even streamed this game for 6 hours on saturday without an issue. I stream at 1080p 60fps with a bitrate of 3500kbps. I did this using the software encoder set to very fast and I was getting smooth clear graphics. The next day, opening a stream while playing the game and the video player in that window stops responding, try and stream and I get encoder overloaded error messages and the CPU usage on core 0 goes to 100% while the game itself is reporting 20% cpu usage, fire fox/chrome claim to be using 3% of the CPU as well as OBS floating between 0.5% and 4% while it's broadcasting. I've tried various things, adjusting OBS settings, adjusting browser settings, using compatibility mode on FFXIV, running it as an administrator to no avail. I even made sure there were no "game enhancing" software like Nvidia Experience or Windows Creator Update installed since people have been reporting issues with those programs. Below is a post of my system information for troubleshooting purposes. I'm hoping someone here has had this issue and got a fix for it.

Operating System: Windows 10 Pro 64-bit (10.0, Build 14393)
Motherboard Model: Gigabyte AX370-Gaming 5
BIOS: BIOS Date: 04/07/17 16:44:40 Ver: 05.0000C
Processor: AMD Ryzen 7 1800X Eight-Core Processor (16 CPUs), ~4.0GHz
Memory: 32768MB RAM
Available OS Memory: 32716MB RAM
DirectX Version: DirectX 12

Have you somehow set your processor affinity to only use one core in FFXIV?

Thanks for the reply, I thought that might have been the issue but when looking at the process in task manager and selecting cpu affinity "use all processors" is checked. I even tried putting the process on a specific core to see if that might have any improvment, but when I put focus back onto ffxiv I can see the core I put it on drop to almost 0% used and core 0 spike up to 100%. It's very strange and I have no clue how to fix it. It had done something like this a few months ago that made the game unplayable on stream so I just didn't stream it, then a few months later when I got my new CPU I tested it out and it was working again. At the time I assumed it was just my old CPU and GPU couldn't handle the game, but I'm running on a pretty beefy system now and even putting the game on it's lowest supported resolution and settings and it still happens. I knoiw there are some programs that can interfere with system performance like Windows 10 Creator Update or Nvidia Experience/Raptr but I don't have any of those programs installed on my computer.