When i use my enderman farm i cant help but notice the endermen teleporting into the void for no reason. I recorded it happening to make it clearer.:
https://www.youtube.com/watch?v=BpmisWSKpII&feature=youtu.be
if you want to recreate the scenario, my farm is identical to the one in this video:
Environment
Enderman farm in 1.14 Pre-release 5 in the end. My operating system is windows 10.
Duplicate of MC-144904