Realm disconnect issue

Hello,

my friends decided to open up a Realm. Everyone can play without any problems except me. I keep on getting disconnected every 1-10 Seconds after I log in. Its unplayable for me. The error message says: "Internal Exception: java.io.IOException: An existing connection was closed by the remote host"

I've tried to far:
Allow Java completely in my Firewall
Disable Firewall entirely
Update Minecraft
Restart my PC
Restart the Realm
Reinstall Minecraft

I have no VPNs nor any other connectivity changes running.
I've followed also all steps on your Guide (https://help.minecraft.net/hc/en-us/articles/360034754132-Minecraft-Realms-connection-issues)

Normal Servers work fine, its just realms. Everyone is using the 1.16.4 Version and is playing on Windows 10.

I noticed that, if I connect with an IPv6 Address, I get disconnected immediately. If I use mobile data or IPv4 it works fine. So its probably an IPv6 issue. 

 

Thanks for your help!