Big glitch

Ive noticed that over the past few weeks some of the pokémon I have are disappearing from my possession and but still register that I have them in the pokedex. It really annoys me because two days ago I evolved Seadra into a Kingdra and then now its just a horsea and have to re-evolve it. This also happens with a Gengar which disappeared,and a bayleaf, which disappeared.

Pigerchou about Pokémon GO, v1.39.1