I've had a problem like this with KODI before
I don't remember what image I was using? I'm sure it was not openvix?
But I found that if I opened up KODI, then backed out of it, the sound would come back.....
But if I rebooted, I would lose the sound again....
I would have to open KODI again and back out to get sound back....
Don't know if this will help you with yours or not?
When this was happening to me, it was very annoying........
I no longer have that problem, I suppose a different image probably fixed it?
Anyway hope this will be of some help to you...
GOOD LUCK..!!!!
Al