Volume issue in CarPlay and Android Auto on Mazda Connect?

2016 CX-9 Signature/2015 CX-5 Touring/2013 MX-5 GT PRHT
I posted in the CX-9 forum, but haven't gotten back any response. Decided to post this here as well.

I have Mazda's retrofit kit installed for awhile now. Other passengers and myself notice that when playing Spotify or Pandora music in CarPlay or Android Auto mode, the volume decreases by itself over some unknown amount of time, but the volume level or indicator stays the same.

Example: I have the volume set to 7. After awhile it plays muffled as if though the volume is a 3 or 4.

The solution is to turn the volume knob up again or if I am using navigation, wait for the navi to give guidance and then the audio volume seems to re-correct itself.

There's no difference if I am using Bose CenterPoint or AutoPilot or not. It doesn't seem to behave this way when using the radio in Mazda Connect.

Is anyone else experiencing the same issues on their retrofit kit installed Mazda?