It has been explained to me that unwanted buzzes are a cause of lips “fighting for supremacy”. Meaning that when lips are buzzing one lip is always dominant. When they are exactly even it sometimes causes a ‘double buzz’ especially with a pinched embouchure.
Simply try pivoting the horn up or down to see if this removes the double buzz.This has worked with my students in the past. I get them to play a note and pivot slowly up and down.
It’s hard for me to reproduce this double buzz problem when pivoting with my MTM embouchure, but easier with my old embouchure (ouch!). Greg teaches a more open aperture so this limits double buzz problems IMHO.
If you are still partly using a “pinch, press and pray” embouchure with your bottom lip behind your top and you are trying to push your jaw forward to straighten the airstream without spending the time on Greg’s techniques and thinking about the airstream angle, you may cause double buzzes as well. i.e progressing too quickly through the system. Not saying you are doing this, but a possibility without seeing you.