The average ticks per second in the latest pre-release is lower than usual. Old worlds as well as new worlds are affected. This was not an issue in 1.13-pre4.
This can be reproduced by using /debug or lighting TNT and observing the delay for it to explode. Eating food also takes a while.
Game can't keep up with normal game tick rate
Mob motion slow and jittery
Underwater block lag
Slower game ticks