I'm having the same problem, and it's kind of intermittent. It is somehow related to the CSSU kernel. At first I thought that the problem was due to some incompatibility with the mafw-eq-renderer-plugin that I installed. I proceeded to reflash the phone with the vanilla (the eMMC) and then with the combined image, and finally the CSSU update. I can give more details, but this is basically an unaffected installation.

The symptoms are that on some calls the earpiece doesn't work, and I cannot listen to the other party unless I switch on the speakers.