I see some minor differences between MediaInfo's audio properties for that "problem" file and one of my own (MP4 file exported from Studio 25 (25.1.0.345 Ultimate))
In my "working" file (that does show audio waveforms in the timeline and in the "noise reduction" tool):
- Format is shown as AAC LC
- Format/Info is shown as Advanced Audio Codec Low Complexity
- Channel Layout is shown as L R
I don't know whether the differences in the problem file are really due to weird settings in its metadata, or whether those differences are false and caused by using a different (much older) version of MediaInfo - I tested using 21.09 and also 22.06 (the latest).
Regards,
Richard