Mail and Message alert sounds and banners don't work when external display is connected to MacBook Pro 16"
I just bought a MacBook Pro 16" which I use in conjunction with an external monitor by plugging both into a CalDigit TS3+ Dock. I used the MacBook Pro for a few days while I waited for an HDMI > DisplayPort adapter to arrive, and everything was working fine. When I plugged in the external monitor, for some reason, the alert sounds and alert banners for the Mail and Messages app did not happen when the external monitor was plugged in. Disconnect the monitor, the sound play and the banners appear. Plug it back in, they don't work?
I tried resetting NVRAM, SMC, re-starting a million times. I checked and re-checked Sound Preferences, Mail Preferences and Audio Midi Setup. I spent an hour on the phone with a "higher level" Apple tech Support person. Nothing.
What to do?
MacBook Pro Retina