Are you using PowerAmp or GoneMad? You've now mentioned both.
I use GoneMad and my playlists have no issues using M3U. This is not with a Filo, but a very old smart phone, with no SIM card, that I use as a portable player.
Personally I don't know why you're trying to use Filo's player since PowerAmp and GoneMad will (should) allow reverse wifi syncing with MB. Also, from years ago when I had a couple of Filos, the player was really awful. I have no experience, nor have I ever heard of USB Music Player Pro. But again, why bother with these when PA and GM are so much better? -AND- your playlists are working with them.