Internal Exception: java.io.IOException: An Existing connection was forcibly closed by the remote host

Hello,

I try to connect to a server (I already played on for days) and get this Error Message:
Internal Exception: java.io.IOException: An Existing connection was forcibly closed by the remote host

I tried restarting game and pc, reinstalled Java, deleted everything and installed everything new, tried flush dns and renew IP, tried different DNS server, tried to start with disabled Resource Packs. I have latest Version of the Launcher and Java.
Nothing worked, I still cant connect and I dont know what to do anymore.
Please help.

Its Version 1.12.2 Forge (I couldnt chose it).