Troubleshooting problem with file numbering display

[Budgie]

Minimserver running on Qnap NAS with bubbleds as controller on S6 phone.
Data tagged using Easytag using ID3v2.4 on openSUSE Leap 15.3.

I have a problem with the display of the file numbers on my control point and am starting here.
I have two opera CDs which comprise a complete work and have been ripped to flac. Rather than having to load two albums I have combined the ripped files into one "album" and edited the file numbering so these run sequentially. ie. the first 29 files are numbered 1 to 29 and the second 29 are numbered 30 to 58. (There are 29 tracks in each CD.) I edited the track numbering using Easytag and as far as I can see they all look right on the Easytag screen.

The tagged files have then be loaded onto the NAS and I have rescanned in minimserver and on BubbleDS and the control point shows all the tracks in the one album but the numbering of the tracks after 29 is showing 13. 42 -
14. 43 - and so on up to 29. 58 and then 1. 30 - 2. 31 up to 12. 41 -

I can sort of understand what I am looking at but cannot see any reason why the numbering is as it is. Is there an automatic numbering system somewhere in minimserver which is being confused by my tagging?

Grateful for guidance here please.
Budgie.