I've used polyphone for about a year now, and it's a very useful tool for creating good soundfonts with very few issues
However, I imported a large amount of .flac audio files, and for unknown reasons all of them are shown as 0.000 seconds long along with the preview being unavailable (seen in attachment), despite the files playing just fine outside of polyphone.
This could be because all these files were previously .ogg files that I mass-converted to flac using vlc, as I lacked the patience required to convert each one individually, as well as the fact that I've only ever used .wav files in polyphone until now, however I don't see how either of these factors would cause it to behave in this way.
This should be working. Could you please try to load only one FLAC file just to be sure there is no interactions with the multiple selection? If this is still not working, could you please share the FLAC file so that I can investigate?