I encoded this particular file within level 5 encoding and the player is unable to show the running time. The file was encoded from a CD. I’m not sure why the specifications for the players list a particular “bitrate” range.
After reading your question, I decided to learn more about FLAC encoding. With an easy web search I found this interesting article written in 2014:
I can imagine that the Clip Sport processor may not be up to the challenge of decoding FLAC Level 5 compression ?
Just for curiousity, have you tested the Clip Sport playback on a few files at FLAC Level 0 or Level 3 ?
(Suggested by the author of this Flac compression comparison article.)
While different FLAC encoder settings will make the encoder work harder to compress the file, they don’t the decoder used to play back the file. The decode process is the same no matter what settings you use to encode, which is one of the main benefits of flac (many other lossless codecs do not work like this).