I can hear only myself when answering a call

Hello,

I have an iPhone XR and when I answer a phone call I sometimes hear myself and only myself. The caller will hear me fine but I can't hear him. This does not always happen but only from time to time and I can't reproduce it at will. It also happens with our without headphones.

What is weird is that when I hear my voice from the speaker there is no latency, it's just like what I say in the mic is immediately transmitted to my speaker.

I have not found anybody with this same issue. Is there a fix? Besides restoring the iPhone? It's still under warranty by the way.

Many thanks.