Me, my sister and her fiancee were playing through LAN on a server hosted by my old Asus laptop. My old laptop can easily handle hosting a server for us, we seldom have any problems with lag. While playing, we started experiencing pretty bad lag (blocks popping back into place, mobs not taking damage for several seconds, etc.) and I decided to restart the server with the launcher open to view the log.

Upon rebooting the server, we started having problems again almost immediately. I pulled up the log and saw that it threw a fatal error and to report it to Mojang. I am including copies of both the Game Output log for my server account and the launcher log. I can provide more information and/or files as needed.