Maybe the Clip Sport (and CS Plus) are not properly accessing variable bit rate audio files ??
Typical constant bit rate choices for mp3 files are 128, 192, 256, 320 etc. I have never observed constant bit rates of 242 or 243.
Maybe check to see if your Amazon audio files are mp3, variable bit rate ?
Maybe consider converting one file to a constant bit rate of 256 and testing playback in your Clip Sport and CS Plus ??
Are you using mp3 files extracted from YouTube mp4 files?
