Connestion lost with server on joining. This didn't happen immidiately but a few minutes later when i tried to explore already created land with a lot of passive mobs in it.

The server map was created in version 15w41a

Error does not happen in singleplayer

Reverting server to old snapshot, renders all animals invisible. This will not fix with an old backup of the map. Only a new server folder where the map and server.jar is copied over, is the invisibility fixed.