Evidently, I’m not alone with AirPods mics not working properly — now for the second time (or even third)!
It use to start with that the person I’m talking to on the phone says: “Sorry, I can’t hear you.” Surprised, I ask them again, “Can you hear me, now?” After some movements they say “Yes” and you think the problem was only temporary. Over time though, the problem worsens and when recording a voice memo it’s totally clear that the signal is not at all clear.
Just before the warranty expired I handed my previous ones over to my Mac store for service. After some days I got a new pair, because the old ones could not be fixed.
Now, only 7 months later(!), I’ve gotten the, too familiar remark again: “Can’t hear you” and recording voice memo “proves” that there is very low level on the microphones, only the left for now, but I know what to expect. If I shake my head a little (no, I don’t hear any better 
) suddenly there appear to be a better connection and the mic signal level is fine — for a while.
My AirPods look like new but my guess is that there is a construction weakness that causes the mics to disconnect after some time. (Some weeks ago I was able to fix a faulty spacebar, even though the warranty was still valid, because I could not wait, but that is a totally different story and can’t be repeated with the new AirPods.)
I’m really not used to this low quality from Apple, but what to do? Are AirPods Pro more robust?