At least once every lesson, the sound does not happen for "type what you hear "
I've noticed this problem, sporadically, in the German course too. It seems that certain exercises are broken, for whatever reason.
I don't know what can be done about it. I reported the same exercise twice to the DuoLingo team, a couple weeks apart, and I received no response and kept encountering the problem. I have since given up practicing the German course for multiple reasons (that wasn't even the biggest problem! It got super glitchy for me several months back, and was doing things like giving me the same sentence over and over again.)
I cancelled my paid subscription some time back, because I was so frustrated at the complete lack of response to the bug reports I submit and the way 90%+ of them would go un-addressed.