Audio not working for German 1000 words

1000 words of elementary German, iOS, iPhone7
some of the audio files seem to be missing/ not playing.

Very annoying when app asks to “Type what you hear” and I can’t hear anything. Some words are ok, others aren’t.

Examples with no audio today, on “Type what you hear”:
alle
Auf Wiedersehen!
der Streit
sechs
BuSgeld

And on “Pick the correct answer for the above”:
us
to sleep
language
also