Audio works in TV/Movie but not in Music/Videos

Running Kodi v16, and recently (after a QNAP firmware upgrade), the audio stopped working when playing certain files.

Everything in TV/Movies works fine, but for some reason all my Music and Videos files don’t play any audio. There aren’t any errors, it looks like it’s playing, but there is no audio. (Audio is via HDMI out.)

In the system audio output settings, it’s set to 2.0 optimized, no passthrough. I’ve tried both the options for output device (PulseAudio Sound Server and HDA Intel PCH), and it doesn’t make a difference.

I’m not certain where to start troubleshooting here. Any ideas?