Server not responding?

[jjplay175]

Okay so this issue is making the game unplayable, i'm playing lan with just me and my brother and the problem is on some chunks say... we played in the same area for a few hours and 0 problems

We adventured left and after we got past a point the server would stop working when ever my brother was there... so i restart server and i'm crafting in my house, he joins and server stops responding so i had to tp him to me

Then i went into the void thing and fell off which took me to that dark land thing, i escaped and it tp me to a place on land and after i went there, server stoped responding

Thing is, i get 0 errors but the server stops responding for a while so i can't exit, save or anything but after a while i can save it and close it but why are some chunks breaking my server?