Unable to enhance audio on mp4 file that was uploaded

Hello - i'm new to adobe and have been testing short (less than a min) mp4 files to enhance audio. I've noticed when I upload an m4a (audio only), I'm able to enhance the audio just fine. It does not work on mp4 which has a video as part of it. And I'm on the premium plan. 

Anyone know what I'm doing wrong? Or is this truly a bug.