Unified the track logic. Seems to work much better

src/indexer.rs

@@ -107,7 +107,11 @@ async fn process_file(
         bitrate: Set(meta.bitrate),
         file_size: Set(scanned.file_size),
         fingerprint: NotSet,
-        musicbrainz_id: Set(meta.musicbrainz_recording_id),
+        musicbrainz_id: if meta.musicbrainz_recording_id.is_some() {
+            Set(meta.musicbrainz_recording_id)
+        } else {
+            NotSet // Don't overwrite existing DB MBID when file tag is missing
+        },
         artist_id: Set(artist_id),
         album_id: Set(album_id),
         file_mtime: Set(Some(scanned.mtime)),