Here is what I do:
1) Start MMA (free version)
2) Choose Options from the 3 dots menu
3) Choose library folders
4) Press + on Internal Storage
5) Choose > Music > Album > Music> Artist
6) MMA Displays list of folders
7) Choose any of the folders
MMA says no files in this folder
If I follow the same steps in 5) using the Files app on the M5 every folder that appears as in 6 has files in it. Some folders have FLAC, some have MP3.
And as I point out in every post, your competitor Poweramp found the files with a simple "Scan for files" step.