On my island I had gotten a lot of mooshrooms, sheep and snowman by buying them with grass blocks. I hadn't been online in a while but one of my friends said that all the animals had just disappeared. I went on and they were gone. I got my snowman back but I don't have enough grass blocks to get my other animals back. I asked everyone that I shared my skyblock with if they knew what happened and many of them hadn't even been on recently. My friend said they disappeared at least a week ago with no sign of what happened to them. If i could get at least two mooshroom and sheep spawn eggs back, I would greatly appreciate it since it took so long to get them in the first place.
Assuming this is for skyblock.net, spawn eggs do not work. And animals/mobs usually despawn around 100. Ask a skygod to spawn some mobs in for you.
Under the trading villager for spawn eggs there is a sign, the sign says basically if you exceed a certain amount of animals lag can be created so the server will remove the mobs without refund. This may have occurred.
Just go ahead and ask a skygod to spawn some mobs in for you, as that is all you can do. If you do have further questions, feel free to private message me