Thank you for posting a follow-up to this confusing problem.
I decided to try your original filenames on four simple mp3 audio files using my Clip Sport (not the Plus version).
I discovered that my player would not display the contents of my playlist using the filenames you reported.
My player would recognize and play the files using MUSIC mode and FOLDER mode.
Then I decided to try a few filenaming variations and I hit upon a solution in my first attempt.
I used “mp3tag” software to create a working playlist using these slightly modified filenames.
B2M01101 -> B2M0101
B2M01102 -> B2M0102
B2M01103 -> B2M0103
B2M01104 -> B2M0104
(I think the problem may relate to using 7 identical characters in a row at the beginning of each filename?)