There have been reports by Reddit users not receiving the baby Pokemon they hatched. I’ve only seen such reports on baby Pokemon. The game will freeze after hatching an egg forcing a restart. After restarting the app they check their journals and see they obtained a baby Pokemon. It registers in the Pokedex still and still shows up under their journals, but nowhere to be found in storage.
Has this bug happened to you? Well, I wouldn’t email Niantic about it. The best thing you can do is report it as a bug. The chances of you receiving the “lost” Pokemon is slim. Emailing Niantic won’t do you any good because they are probably busy responding to several other players, or just busy with the game in general. We all know Niantic isn’t very responsive. They do listen to us… they do, but they can fix this issue faster if it’s reported as a bug.