I had the same and fixed with support from Rdio. Go into config on your server instance and on Audio Conversion select Enabled with normalization. You can try the others too.
Rdio told me this:
There's been issues reported in the past because people weren't using audio conversion or had it disable from the admin / config / options. Note that for audio conversion to work, ffmpeg must be installed on the same host as Rdio Scanner. Audio Conversion will convert the audio to a ACC/MP4 stream which is compatible with smartphones. Some audio formats don't play well on smartphones.
And I toggled those settings and it works on the Android app for me.
Of course you must have ffmpeg installed on the server, which you probably already have.
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