Just recently, I experienced some audio pauses after I-STOP operation and after tons of research and visits to the dealer, we learned that it is due to a sensitive voltage drop detection in the factory-installed audio amplifier. The fix requires a dealer to run diagnostic load tests via MDARS, and if an error is found, they'll order a replacement amplifier from Mazda and reinstall it in the car. More detailed steps are provided in the PDF attached if maybe you wanna go DIY