AirPods stop working with Apple Watch

I've been listening to Apple Music on my AirPods successfully with my Apple Watch alone for several months. It's very liberating to only need my watch, especially at the gym. But just last week, the AirPods stopped playing music reliably.. The music would stop in the middle of a song or at the start of the next one. I can see on the Watch that the song is still playing but I can't hear anything.

There's no problem using my AirPods with my iPhone. It's very reliable.

I "forgot" the device from the bluetooth settings on my iPhone. Reset the AirPods. Powered off my iPhone and my Apple Watch. It didn't help.

The music will sometimes play after a long (minute or more) pause but then it will stop again.