Why does a caller hear their voice echoed when I use the usb-c to headohone adapter?

[Android Central Question]

I have a Pxel 2 XL and when I use my headphones ( MEE audio M6 Pro) to make a phone call the other person hears everything I hear from them echoed back to them.
To clarify, anything that goes through their microphone comes back to them, their voice, any noises, etc.

Troubleshooting steps taken:
Restarted in safe mode - problem still persists
Factory reset - problem still persists
New headphone adapter - problem still persists

Any thoughts?