Hi,
Seems to be that Rec Forge II, it's dealing with problems with not actualization in a close future. But, perhaps yours it's related with your phone model and brand.
For example: In my Huawei Mate P20 Lite. When I mark front or back microphone the option appears, but when I leaved it in "by defect", I have the same problem than you. Perhaps, it's a question to play with the microphone options (rear o by defect) to see what happens.
Cheers,