I'm unable to replicate this with purely the base Origins, but I'm going to try downloading a larger Origins pack (Origins++, ik you're the maintainer of it, and you're probably reporting this based ...

Some Minecraft users see an error message saying Connection Lost, Internal Exception: java.io.IOException, An existing connection was forcibly closed by the remote ...

java.lang.ClassCastException: class net.minecraft.server.network.ServerGamePacketListenerImpl cannot be cast to class net.minecraft.network.protocol.game.ClientGamePacketListener (net.minecraft.server ...