"kawa" is the nominative case - the one you find in the dictionary and which is used when it is the grammatical subject, eg:
"Kawa jest bardzo dobra"
"kawę" is the accusative case, which is used when it is the direct object, eg:
"Bardzo lubię kawę"
Isn’t Polish stress always on the penultimate syllable? It sounds like it was on the last syllable in both lubią and kawę.
It's an error. The pronunciation of 'kawę' is really weird here. I guess that's a charm of TTS'.
Sounds right to me. Just that the intonation goes up on the last syllable of kawę. Intonation is a cue to stress in some languages, so you might perceive it as stressed because of that. Lubią sounds weird I guess. Equally stressed maybe?