I know that Windows can choke at times on characters that *NIX based OSes are fine with, so throwing it out there. I used kid3 running on a Mac to create all of the m3u playlist files. My library is on a QNAP NAS running Linux based QOS. Is it possible that something is using a character that isn’t handled well by Windows?
Nothing changes (same ones come in, same ones don’t).
I also tried turning off “import playlists” in storage, saving, then going back and turning it on and saving. I used kid3 tag editor to create ALL of the m3u playlist files with the same exact options. When I open the m3u playlist files of one that works and one that doesn’t, everything appears to be the same (both just list the file names of the tracks and nothing else/extra. Some of my m3u files in some of my folders get imported, while others don’t. I am having a similar issue, but I’m using relative paths and all of my m3u playlist files are within the folders where the music files are.