I'd maybe enable debug logging in Gadgetbridge and then maybe take a look at the log from Gadgetbridge and see if it's seeing the notifications message that comes in?
But it is possible it's something about Samsung's music player. Maybe if you used some other kind of music player app rather than Samsung's built in one it might work?
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
I'd maybe enable debug logging in Gadgetbridge and then maybe take a look at the log from Gadgetbridge and see if it's seeing the notifications message that comes in?
But it is possible it's something about Samsung's music player. Maybe if you used some other kind of music player app rather than Samsung's built in one it might work?