"He always sleeps afterwards."
Translation:On potom vždy spí.
you were misled by two meanings of always. if he slept "always" as in "constantly, all the time"=stále, it would mean before, during, and after whatever it is we were talking about. so saying potom clashes with the constancy of sleeping. in the sense of "always" as in "every time"=vždy, pokaždé, there is no clash.
as you know, we are still in beta. i am adding your translation, which corresponds to the english sentence delivered with the following stress: He always sleeps afterwards.
czech word order is not a table lookup by word type, so i hope you were not expecting the language to behave that way. such an expectation could become a recipe for disappointment.