Comment 86 for bug 1834771

The problem does seem to have (at least) two separate causes:

1) Failure (during installation and updates) to recognize the hardware and install the right kernel module(s)

2) Adverse interaction between OS components such that the kernel can see and use the hardware, but HDMI audio is initialized in a disabled state

The workaround (which I continue to auto-run at each boot, otherwise no HDMI audio!) only works if 1) is not present. (workaround ref: https://askubuntu.com/a/1207919)

The root cause of 1) might be something as simple as an incorrect hardware ID string; maybe just need a simple patch to fix. But in any case, users with hardware affected by 1) need a fix.