Multiple albums generated from 1 album's worth of files

My wife tried to put on some festive music this morning (Ce Lo Greens Magic Moments), and LMS just queued 1 track. Last Xmas, the album played fine.
LMS seems to have created 6 albums, all with the same name. 1 version has all the 14 tracks, the others have 1 or more tracks seemingly at random.

I went in with Mp3tag to see if there were any strange tags - nothing that unusual, but I simplified it to leave just:
Title, Artist, Album, Track, Genre
with nothing else in Extended tags
I also made sure the Album and Artist fields were the same

I tried a "new & changed" scan, as well as full rescan, but in both cases, I now only have 2 albums of the same name, the first with all 14 tracks, but the other with tracks 1, 2, 7, 9, 10, 13

This album is mp3, whereas most of my music is flac, and the folder structure is ...\<artist>\<album>\tracks

The option Treat TPE2 MP3 tag as Album Artist is set
LMS 8.0.0 1590399854 running on a Pi4 with PicorePlayer 6.1.0

I have tried a scan with logging set to debug for the scanner options, but this doesn't show anything relevant.

Any ideas??

Cheers
Nigel