^Is it possible that one is St Vincent (no period) and one is St. Vincent?
You can use a program like Mp3tag to inspect the tags of the two albums and see if there are any differences.
Also, and I don't know if this would take any effect in the Fiio, but your music program might have the 'album artist' and 'artist' as showing two different names or variation spelling of the artist... like what clee290 said.
My FiiO X1 has alphabetically rearranged two St. Vincent albums I have.
On my PC and microSD card folder, it's arranged:
St. Vincent - St. Vincent
St. Vincent - Strange Mercy
However, on my Fiio X1, it's arranged:
St. Vincent - Strange Mercy
Steely Dan - Aja
Steely Dan - Pretzel Logic
Stevie Wonder - Innervisions
Stevie Wonder - Songs In The Key Of Life (Disc 1)
Stevie Wonder - Songs In The Key Of Life (Disc 2)
Still Corners - Strange Pleasures
St. Vincent - St. Vincent
It's not a big deal, but how can I fix this? Thanks in advance!