There are two mikes in a FP2. One in the bottom module, the other one in the top module. Sounds as the one in bottom mod does no longer work and the one in the top module does. Hardware diagnostics test should show that - as you can test both mikes there.
Btw.: If it might really show that bottom mic is “broken” then you might have a look at Microphone not working anymore as it gives some ideas of workarounds…