Sort by disc
When an album contains multiple discs, the tracks should be sorted first by disc number and then by track number. Currently, the tracks are sorted solely by track number, which means that the album's songs are interleaved resulting in the wrong play order.
As of September 2022, albums with multiple discs are still sorted by track number (interleaving tracks from both discs). Tested with the most recent version, 5.14, in two different devices with Android 6 and 7, with identical results. The albums which cause the problem with Simple Music Player are ordered correctly in other players (i.e., Vinyl Music Player). The albums' tags have both the "Track" and "Position in Media Set" correctly set up (confirmed with a desktop ID3 editor).