The cause was firework rockets, when I shot of a Flight Duration 127 in the nether, it crashed my game, my ms ticks (milliseconds per tick) went up super high, it eventually crashed, so I went back into the world, and quickly killed all the firework rockets, then my ms ticks quickly went back to 10 or so.

(PS. Someone could crash a server with this, they could simply encase it to prevent it from going up too high and despawning, and it would very quickly crash the server unless it had special protection from that)

So I recommend that you optimize fireworks in order to solve this problem

(I also spent an hour trying to figure this out so please do it for me)