This question already has an answer here:
I finally found a Squirtle and caught it, but then the app froze and I lost it.
However, my Pokedex still shows a picture of a Squirtle, but I don't actually have it. This isn't the first time this has happened to me, is there anything I can do to recover the Pokemon that this happened to? Any way I can fix this? Just an annoying bug?