I assume it was right after the server restart but I'm not positive but a lot of people including myself lost our farm/bred animals.
In my case I lost a lot of chickens, some people lost their snow golems and I'm not sure what all was effected. BUT... Obviously there was some error around the time of the last server restart, or maybe this was done one purpose. but this thread is just to notify that there MIGHT be some issue somewhere regarding animals.
The image shows a few people that were effected, but also shows a pig (Wild) that wasn't so I'm thinking it may have been only SPAWNED animals like chickens from eggs and snow golems, but I really don't have any clue why this happened.