When you are having issues in games with a P2P (peer-to-peer) in Windows you might want to try resetting your DNS-cache. It fixed high ping issues in Garry’s Mod and Risk of Rain 2 for me.

Resetting the DNS-cache

Press the Windows-Key, type cmd and hit Enter. A mostly black window will open.
Here you need to type 2 separate commands:

ipconfig /flushdns
netsh winsock reset

Press Enter after each one and finally restart your computer.

These commands will clear your DNS-cache and reset the winsocket programming interface used for the network connection.