Most (but not all) m3u playlists not being imported

My m3u playlists were created with Swinsian, a Mac-based music player. All my music is stored on a Synology NAS. The m3u files do show the correct path to my files, but only 2 out of 13 playlists are being imported. All these m3u files were made at the same time, and they all work when my existing SONOS player scans them. The 2 that are imported also work correctly, so I’m at a loss as to why the others m3u files are being ignored. All these m3u files reside in the parent directory where all of my music files live. All of my music is being indexed properly, and I have no trouble playing anything back when selected directly. I have tried deleting these playlists, re-indexing the library, then re-copying the playlists over, and the same 2 get imported each time.

Do all of the files in the playlist exist within the directory structure in which the playlist is found?

Yes… All the music files are in directories inside the directory where the m3u files are located. For example:
Z:\music\Jazz (directory with many files and directories inside)
… etc…

Hi @Dan_Callaway

Can you share a screenshot of Settings > Storage?

Do these playlists use relative paths or absolute? We recommend using relative paths whenever possible.

The playlists use absolute file paths…

Here is a line from one of the m3u files that are imported… The address is my NAS drive.

#EXTINF:349, Wes Montgomery - A Day in the Life
\\music\mLibrary\active\Jazz/Guitar/Wes Montgomery/[1967] A Day in the Life/01 A Day in the Life.mp3

From Importing playlists:

Looks like you have used a mix of forward and backward slashes as path delimiter. Your paths are absolute but relative paths are recommended.

I did just try replacing the exact paths with relative paths on a few of the m3u files, but that didn’t solve the problem… This odd thing (to me, anyway) is why 2 of the playlists are being discovered, and 9 of them are not. The files are formatted exactly the same.