HDMI audio appears only when turn monitor off and on

Hi, I have an issue where on a computer I am building for customer where HDMI audio on Mac Mojave portion works only if you turn monitor off and on (you do have to have it on during boot to select OS, then once in OSX, turn off and on again). Everything is ok on Windows.
Motherboard is unknown (XCY mini computer), video is built in HD Graphics 6200, cpu is Kaby Lake i3-7200U. Everything works OOB except built in audio.