FPS drop from 100+ to 0

In a server, i am dropping from 100+ to 0 for at LEAST 5 seconds. It happens after about 20 mins, then i have to completely shut down the game, and relaunch it for the next 20 mins. VERY annoying and cant have anything to do with my computer. Clean jar file. Also, I run out of memory when i'm usually at 10% when I try take a screenshot.