So I might look at the settings (menu) on the monitor to see if there is anything that might help.
I want you to know that I spent a couple of hours this morning seeing if there is anything I could do on mine to stop output (if I could maybe that would lead us to a solution on yours). There does not seem to be the option to change the audio output back to the device (other than to use a different cable to connect to the monitor and I do not have any here to test with). That said, I did connect to a Bluetooth speaker and that worked if that is an option for you.
I wish I had more to offer