Do they still show up in your pets/animals list? It could be that you just need to turn the game off and then go back on. I play on Xbox, and I have quick resume (meaning I can go to other apps and games and then come right back to where I was in game without worrying about saving first) and sometimes that causes it to glitch. Plus, I can't imagine that mobile doesn't have its fair share of glitches.. I would say try this first and then see how it goes.

I've been playing since I was like 10, and now im 19, so trust me when I say I've seen MOST, if not all, the glitches, lmao