Music-library folder plays tracks from subfolders instead of its own tracks

I am having an issue with the Sonos app (Android) and a music library stored on a network share.

My library contains a folder named A, which has its own music files as well as several subfolders that also contain music. However, when I browse to folder A in the Sonos app and select one of the songs stored directly in that folder, Sonos plays a song from one of the subfolders instead.

For example, selecting the second song listed in A plays the second song in sub1. The apparent track order is preserved, but Sonos seems to ignore the files stored directly in A. As a result, I cannot play the songs located in A itself.

Example:

A/
├── 01 - Song in A.mp3
├── 02 - Another Song in A.mp3
├── sub1/
│   ├── 01 - Song in sub1.mp3
│   └── 02 - Another Song in sub1.mp3
└── sub2/
    ├── 01 - Song in sub2.mp3
    └── 02 - Another Song in sub2.mp3

Expected behavior: selecting 02 - Another Song in A.mp3 should play that file.

Actual behavior: it plays 02 - Another Song in sub1.mp3 instead.

I am somehow surprises that nowbody seemed to have reported this issue yet. Is there anyone else encountering this?