External subtitle support in SMB

Locally, playing video files with external subtitles from the same directory works fine. However, when playing files from an SMB directory, external subtitles are not being picked up. The video players I'm using are mpv-android and MXPlayer.

For example, the following works:

Local Device/
├─ Some Folder/
│ ├─ Psycho-Pass 3 - First Inspector.ass
│ ├─ Psycho-Pass 3 - First Inspector.mkv

Both video players pick up the external subtitles.

However, this does not work:

SMB/
├─ Some SMB Folder/
│ ├─ Psycho-Pass 3 - First Inspector.ass
│ ├─ Psycho-Pass 3 - First Inspector.mkv

Both video players do not pick up the external subtitles.

MXPlayer's built-in implementation of an SMB browser is poor, but it does properly pick up external subs. So, I'm hoping it's possible with MaterialFiles, as well.