Hi when I reboot the HDMI Audio Playback device disappear.
Note they are not visible when enabling "Show Disabled Devices" or "Show Disconnected Devices".
In the Device Manager the option "Show hidden devices" will show them as disconnected in both "Audio inputs and outputs" as well as "Sound, Video and game controllers".
Reinstalling the "Display Adapter" driver trough the device manager, e.g. right click on "Radeon (TM) RX 480 Graphics", Update Drivers, Browse my computer for driver software, Let me pick from a list..., and selecting the already installed driver and let it install again will make the HDMI Audio devices work again till the next reboot.
I already tried a clean uninstall with "amdcleanuputility.exe" and a reinstall of Catalyst 17.4.2. Still having the same problem.