I've been monitoring my own servers lag issues and I've narrowed it down to a few things. Opening a book will cause server lag depending on if the server is using an SSD or a HDD (0.28 seconds with a HDD No lag if I port it over to my SSD) I assume this is due to book data being stored in a .TXT file. Opening enderchests for some reason cause server lag (I'm not sure why on this one, The data's stored in a player.dat which is in the RAM so no reason for it. New terrain generation caused a lot more before (Causes my server to drop down to 10TPS if I go flying in creative mode)