This is just an issue with inconsistent tag naming between different applications. The "Album Artist Sort" and "Artist Sort" tags have always been a problem.
The relevant change in MC was in MC23:
https://wiki.jriver.com/index.php/Release_Notes_MC2323.0.96 (1/24/2018)
1. NEW: Added support for the Album Artist Sort field and Composer Sort field to the ID3v2 code (TSO2 and TSOC).
However, that change may not have been implemented for all file types. I'm not sure. See
https://yabb.jriver.com/interact/index.php/topic,122322.msg846744.html#msg846744We load these from ID3 as "Album Artist Sort" and "Artist Sort", but we do not have built-in fields for them. If you create "Album Artist Sort" and "Artist Sort" custom fields, they should be populated. I do need to add them to FLAC and maybe other file types.
I don't know if that extra work was ever done, or even required.
This is not a new issue:
https://forum.dbpoweramp.com/showthread.php?36252-FLAC-metadata-conventionsThe issue has always been that some applications use the name without spaces and some include spaces in the name. MC can't force a standardisation of naming, particularly if different people are tagging using different applications. i.e. mp3tag, DBpoweramp, PerfectTunes, etc.
Work out which format your external tagging tool uses, and use that in MC. Or set up both versions in MC and have one populate the other if the version you want to use in empty.
Note that the name of the tag can be different to the Display Name of the tag. The name must be used exactly as it is in the source file for MC to import it. The Display Name doesn't matter.
Note also that tagging in MP3 files can be different to tagging in FLAC files, depending on the external tool.
Note also that mp3tag for example can use tag mapping, and some use code, so that the "ALBUM ARTIST SORT" tag populate the "ALBUMARTISTSORT" tag.
With a little research I'm sure this can be solved, or it can be shown that MC functionality has changed without notification. Look into it a little deeper.