We started testing new voices (Google TTS) and I am quite confident that they will soon replace the old ones. Therefore I don't think there's much sense in reporting issue for the old voices, I believe they will soon be gone.
In plural there are only two genders, virile and nonvirile. Nonvirile adjectives such as smaczne do indeed have the same form as in the neuter singular.
Technically the first sound of "ciasteczka" is "ci", not just "c". That's the same sound as ć, which is a palatalized sound. I think it may be similar to 'ciao', but I'm not entirely sure.