Server refresh errors and other misc problems

Motherboard - ASROCK EP2602
Memory 16 GB (x4 4gb sticks) DDR3 SDRAM PC3-12800
CPU - (x2) Intel Xeon E5-2670
OS - Windows 10 Pro
Internet - ATT Fiber 1000
Plex Version - Version

To keep this simple I will just post the issues

  1. At first my server wouldn’t play 4K videos, it would say the connection isn’t fast enough. To fix this we hard wire in both the server and the media box (Roku Ultra).

  2. If it wasn’t a connection issue we would get the error saying the video wasn’t powerful enough to transcode the video. We have tried every option we can find online from direct connect, to changing the quality and so on.

  3. Even TV shows at 780p will struggle to play with constantly buffering or erroring out.

  4. Most recently, we noticed that even though the server his hard wired into the modem, with a cat 6 wire, we are getting around 400 to 600 down and 900 up. Every other computer hardwired into the network is pushing around 900 down and 900 up.

From my understanding, this build should be able to transcode if need be, this setup should be able to direct connect and the speed shouldn’t be an issue. What am i do wrong?