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

So, I've made a 1.12.2 server for me and my friends to play on, they're able to join but after 2-5 seconds they're kicked out with th above error and I have found out that it's completely random(sometimes they can join and not get disconnected) but that chance of it happening is high. We did some digging online and people said enable the app through firewall, reset your router, check you correctly portforward the game but nothing fixed until we switched to verison 1.12.1, this is where everything worked completely fine.