Pixelmon server problems

My friend has made a pixelmon server for our friend group and it worked just fine the first week. however, later on we found that pokemon, chests, and characters would be turned upside down, and inventories would go invisible for a few seconds - things like that - started happening when we were around the server owner's player. when we were far away from him it wouldn't happen, and when he is logged out it doesn't happen - it only occurs when we are close to his character. Any explanation as to why this happens or any way to fix it? We have tried restarting the server, moving the server's host to a different location, etc etc and cant find anything online about it. Help would be greatly appreciated!!