Slimserver: : media scan fails to index most of the files

I just did an upgrade of my home server and I switched from slimserver at version 7.9.1 (using perl 5.30.0) to unstable’ version 7.9.2 (using perl 5.34.0) and as soon as I did a new re-index I discovered that the new version indexes just so few audio files. I did a “controlled test” with a tree of folders that has 7707 files of which 6042 are audio files (all flac), with the logger for the “scanner” component set to “DEBUG” I’ve collected these logs:

[...]
[21-09-02 22:19:44.8323] Slim::Utils::Scanner::Local::Async::__ANON__ (81) Async scanner found 7678 files/dirs in 17.41 sec
[21-09-02 22:19:44.8351] Slim::Utils::SQLiteHelper::updateProgress (442) Notify to server: [
  "progress:1630613967||importer||/mnt/musica/lossless/classica|discovering_directory||7678||7678||1630613984.83304",
]
[21-09-02 22:19:44.8483] Slim::Utils::SQLiteHelper::updateProgress (466) Notify to server OK
[21-09-02 22:19:44.8494] Slim::Utils::Scanner::Local::__ANON__ (192) Start processing found tracks
[21-09-02 22:19:44.8505] Slim::Utils::Scanner::Local::__ANON__ (200) Connect do DB
[21-09-02 22:19:44.8513] Slim::Utils::Scanner::Local::__ANON__ (203) Get latest ID
[21-09-02 22:19:44.8526] Slim::Utils::Scanner::Local::__ANON__ (225) Delete temporary table if exists
[21-09-02 22:19:44.8536] Slim::Utils::Scanner::Local::__ANON__ (228) Re-build temporary table
[21-09-02 22:19:44.8793] Slim::Utils::Scanner::Local::__ANON__ (277) Get deleted tracks count
[21-09-02 22:19:44.8802] Slim::Utils::Scanner::Local::__ANON__ (284) Get new tracks count
[21-09-02 22:19:44.8814] Slim::Utils::Scanner::Local::__ANON__ (289) Get changed tracks count
[21-09-02 22:19:44.8823] Slim::Utils::Scanner::Local::__ANON__ (295) Removing deleted audio files (0)
[21-09-02 22:19:44.8830] Slim::Utils::Scanner::Local::__ANON__ (373) Scanning new audio files (444)
[...]

So the scanning finds out 7678 interesting files (audio files, directories, playlists, .cue, etc) but in the end just 444 got indexed. All this staring with an emty /var/lib/slimserver.

Anyone has any suggestion about how to find out more?
cc @phile314