How to make sure artists appear under their last name on Apple Music?

This is a problem I cannot seem to fix no matter what I do. For my music library I use iTunes, and then sync that library to my iPhone for listening on the go. For some reason, one particular artist will not appear under their surname in my iPhone's artist list. The artist in question's surname is O, and therefore they should appear under O. Instead, they consistently appear under their first letter of their first name.

I have:

Done all the artist info > sorting for their name as beginning with O, for artist, album artist and composer fields

Checked any appearances in a compilation I have, and done the same for sorting there

Checked data in the properties of my iTunes folder on PC

I am at a loss of how to fix this. For some it may seem unimportant but I take a great pride in my iTunes library and its presentation! It's my OCD. Worst of all, this issue has occured before with other artists, and after a complete reset and re-sync of my iTunes, it was fixed all but for this one 'O' artist. Very confused. Ive theorised that since they were the only one of the mis-alphebetised artists to appear in a compilation outside of their albums I have saved, that may be the cause. Is that likely? If so, will another re-sync be needed?

Please advise!

[Re-Titled by Moderator]

Original Title: Alphabetising Issue on Apple Music for iPhone