Created an enderman farm using an endermite to attract endermen into an area for the player to kill. The endermite was named and in a minecart, yet after unloading the chunks for only a few minutes, the endermite had despawned. It didn't even require unloading the chunks, as I sat at the farm and had it disappear while I was there twice.
Thank you for your report!
We're actually already tracking this issue in MC-27535, so I resolved and linked this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.