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Just came accross this issue myself with a private server hosted world. 
I have duplicate Bees spawining. I have removed the spawn blocks but the bees have started to respawn and also duplicate so there are far more bees than originally there. This is causing major lag at my base. If I move away from the base the lag dissapears. Not sure if there are other entities with the same issue but I cannot kill any mobs within my base to help alliviate the bug. When I asked the server admin to run a kill command on the bees the lag subsided (didn't go away fully) and the bees dissapeared. This kill command was run for 15 minutes and over 400 bees reportedly were removed, thats what the admin said, and it was still ongoing but I had to log off.  Upon relogging the bees are back again and the lag is back to how it was before the kill command. These bees are in a villager farm if that makes any difference. The issue, for me at least, appeared after the last update.

Experiancing the same issue on a server someone I know runs. I have about 6 hopper minecarts running, moving various items around. I've been requesting reboots of the server almost daily now. The reboots fix the issue for a little while but then it happens again, the minecarts stick in "random" places along the tracks. I have tried turning all of the minecarts off before leaving the world or even the tick distance however this does not help in my case. The server is running on a linux machine. This was happening before the latest update, however the issue is more frequent now since the update.