As described above, Endermites appear to move really fast once spawned with an enderpearl. This only appears to happen once you exit a world and reenter it.
STEPS TO REPRODUCE:
1. Enderpearl around until you spawn an endermite
OPTINAL: Equip a sword
2. Exit the world
3. Switch the gamemode to Survival
4. Reenter the world
5. Try to kill the quickly moving endermite
NOTE: Most of the time it happened, but if it does not, try again.
I apologize for the lack of screenshot, but how can you screenshot a fast moving endermite? (the method of screenshoting on my device is the way you screenshot on IOS)
P.S I looked if there was any like this, but I found none. I am sorry in advance if this is a duplicate.