If you have trouble locating things that have disappeared or previously stored, please check the Storage.
Be sure to check all of the tabs indicated in the storage. There are currently 5 tabs in the storage. These are for Animals, Kiosks, Decorations, Maps, and Buildables. By clicking the correct tab you can find the item you are looking for! You can also use the search bar!
Note: Upon completion of a seasonal buildable, they will be located under the Buildables tab if you don't see it on your island.
If you are gifted or upgrade an animal you own already, it will not show up in Storage but add to your existing count.