I was giving potion to my pokemons when i was farming and accidently it was given to wild spawn!! and after that i cant throw pokeballs at them ! even after refreshing the same issue exist!!
you accidentally used a potion on a wild poke, and then weren't able to throw pokeballs, even after relogging. you were pretty clear as far as im concerned xD
i had a similar issue recently but i didnt realise that/dont know if it was through healing wild poke. it cleared itself up pretty soon though