AirPods Pro Microphone Stops Working mid-call

Hi,

My AirPods Pro are working great for listening to music or just blocking out noise. When used on a phone call, however; they work fine for a few minutes after which the microphones turn off and the person I'm calling no longer hears me, although I can still hear them. If I toggle to the Speaker, the 2-way audio works again (via speaker and the phone's microphone). Toggling back to the AirPods and the audio still only works for receiving and not sending audio.

iPhone 11 Pro

iOS v13.2.3 (17V1111)

AirPods Pro HW 1.0.0, FW 2B588