He said it did not... He tried a factory reset and had issues then got swapped and still an issue.
I have the exact same issues described and if you look a few messages up it seems to have to do with the voice assistant via bluetooth that is somehow involved in this.
If you have exact symtoms, audio is playing and timer is moving but you have no audio in BT try doing whatever would trigger the voice assistant via the headphones.
For me when i have the above, if I long press my surface headphones, or triple tap my soundpeats (both are buttons to activate hand free via headset) the audio starts coming out like it should.
The above cures the issue when it happens, but so far I have not found a cause.
One thing does cure this but its a bummer as it involves turning off "phone calls" option in the bluetooth menu for the devices having this issue (I have confirmed an issue for all 3 of mine, Car, Surface Headphones and Soundpeats earphones)
The downside of doing to above is you cant use them for phone calls or video meetings.
I was really hoping the next update would address this but just updated today and can confirm the issue is still there, so I guess I will now open a ticket and see what they say as Dan has already done.
I did use the feedback option in the settings of the Duo 2 to provide a bug report to MS while having this issue, but not sure if anyone even looked at it ;-)