Game stutters when players join on LAN, After a while the stuttering becomes permanent.

I've been hosting a LAN game for months. One night a friend joined on his xbox and we both experienced severe stuttering. It stopped when he disconnected and started when he joined again. He quit again and I played solo for about 15 minutes and the stuttering came back and became permanent and the effect worsened until almost nothing loads. Just a spider and a painting hanging in the air.

A few days later the exact same thing happened in another world when a friend joined on her laptop.Stuttering when she joined, stopped when she quit, short time later became permanent.

We've had no problems for many months until now. We were mining and building when it happened. Nothing out of the ordinary.

Also f3 + c wont crash the game.