From my experience, somewhere in 2017 I have noticed that the audio quality of video that had music in it dropped and was very bad. It was very obvious for the sound of cymbals of the drum. I was not sure if it happened on android only or on other platforms as well.
Still, in 2019 (I edit this post) I have listened to music videos people uploaded on Instagram and the quality has not improved. There is no noticeable difference in audio quality if it was not a song.
A way I discovered after asking in forum for advises was to change the audio to mono. This only requires simple editing. Use any editing software such as Sony Vegas Pro or any other that supports audio editing to change stereo to mono. To do this, simply just combine left channel and right channel of the audio.
When combining both channels you will notice that the audio has lost some details as you cannot hear stereo anymore, however it will sound better on Instagram coming out of the speaker compared to the unedited ones.
When combining both channels you will notice that the audio has lost some details as you cannot hear stereo anymore, however it will sound better on Instagram coming out of the speaker compared to the unedited ones.