Server Version#: Ubuntu 1.25.8.5663-e071c3d62
Player Version#: Windows Version 1.42.1.2926-415b0e14
On my Windows 10 Plex for Windows Player, the sound is output through “Line Out” instead of over “HDMI” to my Dell S2721DGF monitor which then plugs into external speakers. Even though I have my sound set to go over HDMI.
On the same system, I can load up FireFox and put in my plex server url and it plays audio over HDMI fine. So it appears to be a Windows Plex Player issue.