I can’t say why SF uses YT Plus Downloader instead DRM M3U8 Downloader ..
.. but I can say that Audio is detected and downloaded:

Looks fine but I can’t hear anything, because:
Bitstream parsing ran out of data to read before the end of the syntax was reached, most probably the bitstream is malformed (conf, offset 0xC26D)

So it’s the same as with tv4play using DRM M3U8 DL here
btw: Using mp4 with “Fast Start” or mkv(mkvtoolnix) change nothing.
I dl manual first + last m4s Audio segment and they have same size ..
.. therefore, I suspect the problem occurs when merging the segments.
edit:
StreamFab 7.0.0.9 Changelog
Fix: A problem that downloaded videos from some M3U8 sites have no sound during playback.
=> SF 7009 fix the problem ! √ checked