AirPods not taking calls

My AirPods 1st gen firmware 6.8.8 work perfectly except when taking phone calls: I can hear the caller but the caller can’t hear me.

Doesn’t matter if I’m on WiFi or cellular.

I also know for a fact that it’s not on the receiving end: As soon as I take out the AirPods or switch the audio input to “speaker” or “iPhone”, the caller can hear me perfectly.

However, every other time or so the AirPods do work as intended and the caller and I can both hear each other.

There are no issues when speaking to Siri or using dictation, recording voice memos, etc., so I know the microphones aren’t physically damaged.

Is this a known bug or did I get a “bad Apple”?

*Yes, the iPhone is unlocked when taking calls. iPhone is a 2nd gen SE on iOS 13.5