They should be sorted by the total amount of time spent playing that album on this profile, measured in seconds.
The time-based calculation is new in 1.3. The old algorithm looked at play count, which falsely inflated the ranking of releases made up of tons of short tracks. One listen to Bartok’s Mikrokosmos (72 minutes, 96 tracks on my recording) was receiving 19 times as much weight as one listen to Beethoven’s 9th (5 tracks, 67 minutes), when in fact they both represent approximately the same amount of investment into the material.
For people with broad collections, this tended to inflate the rankings for genres with shorter tracks (3-minute pop songs) at the expense of genres that lean towards longer forms.
We received a lot of complaints about this, so we re-designed the ranking algorithm for albums in 1.3. We went through many iterations on this in alpha before landing on this solution. It wasn’t done lightly or carelessly.