Minecraft Server Timeouts for 2 specific people out of 5

[glados9999]

Setup:
Server (Linux Mint)
Clients (4xWindows 10 and 1xArch Linux)

Lets focus on one Person (Windows 10), at first he used a Firewall which did block receiving some things, Teleportation didn’t work except he rejoined. After disabling the Firewall it worked for a few minutes and didn’t time out. Teleportation did work always instantly without issues. But he does still randomly timeout. Sometimes in a second or a minute. He uses LAN.

For other 3 People (2xWindows 10, 1xArch Linux), everything works perfectly fine.

Here are some more information I could grab through Discord Screenshare.

[glados9999]

Seems like he plays with us, he is able to play for much longer but still times out at some point randomly. He Changed is DNS Server from 1.1.1.1 to 8.8.8.8, also rebooted his PC and mentioned that all this helped a bit. Sometimes he times out instantly, sometimes it takes a lot of time.