Player gets kicked from self-hosted server randomly between 5 and 45 minutes (Forge 1.20.1)

Hello there!

I'm going insane right here:

I am hosting a server for me and a friend of mine with a custom modlist. I am connected via localhost and can play without any issue, but my friend gets kicked with the "internal exception java.net.socketexception connection reset" error randomly inbetween 5 and 45 minutes and gets locked out for somewhere inbetween 5 to 10 minutes.

I'm trying to fix that issue for 6 hours now, but can't get it to work.

the custom modpack in use: https://www.curseforge.com/minecraft/share/kEHM_GCz
the mod on the server are identical with following exceptions:

embeddium-0.3.31+mc1.20.1
lighty-forge-2.1.2+1.20.1
oculus-mc1.20.1-1.8.0
those are not installed on the server, since they would cause the server to not start in the first place.

there is no crash/error code in the server log nor in the debug log

I already tried the following "fixes" on the remote PC:
lowering simulation/viewing distance; disabling LSO in windows; flushing/renewing dns cache in the command prompt; fixating dns server adress to 8.8.8.8 // 8.8.4.4; reinstalling minecraft and the modpack; reinstalling the server; even resetting the computer to factory settings and building everything up from scratch

(also configuring inbound rules in windows defender firewall on the hosting PC)

Side note: The remote PC was seemingly always able to connect to other public servers normally without getting kicked. I tried the fixes there first anyway, since the error message “internal exception [...]” apparently always indicates a problem with the remote PC.

But I'm pretty sure now that my server is the problem, but I can't figure out why, let alone how to fix it.

The only code I changed in the server files is in the user_jvm_args.txt file:
-Xmx5G -Xms5G -XX:+UseG1GC -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=32m

I hope someone can help me and save my sanity...

Edited September 10Sep 10 by xtherion