I experienced the same issue, and managed to fix it by turning of DVC (direct voice control) in advanced tweaks.
In addition to this, when the MusicFX button is enabled in advanced tweeks, and you go to the volume control panel and toggle MusicFX you can have the benefit of using Dolby, or without it, from within the Poweramp controls. On my phone, however, the toggle switch is swapped around so that, when DVC is disabled and MusicFX is enabled in settings, to use Dolby the MusicFX toggle needs to be set to off. And when it is set to on, dolby is disabled and Poweramp uses its own settings instead. Thus is an issue I will further in a new thread.