Can not get Asset to sort by Surname, First Name

Hi all
Can not get Asset to sort by Surname, First Name
Sort Tag Handling is set to Use Sort To Order Display.
In Browse Tree the Artist container has A to Z and No Track Listing ticked.
All albums which have Name Surname artist have Artist Sort Tag all other with band names do not have Sort Tags
Is presence of Artist Sort Tag required on all Albums to get sorting working or just on some of them ( those with band names will get sorted anyway )?
What am I doing wrong?
Please point me in the right direction
TIA

For which audio format? which program created the sort tags?

All files are flac with some ripped wav (ripped with dBpoweramp) .
For tags I am using dBpoweramp &*8211; select all - right click - edit ID-tag for Multiple Files

changing Sort Tag Handling from "Use Sort To Order Display" to "Display in Sort and Non-sort Locations"
and back to "Use Sort To Order Display" has done the trick.
It is sorting correctly now.:)