I think it began when 9.4 was installed. Each flash of this message is accompanied by popping
4190 is not the latest build available for the 3800 model - build 4200 is.
Check manually at Settings/System/System update/Check now - if it offers 4200, install it and see if this resolves your issue (its being rolled out, so it may not be available for you yet).
Otherwise, what does Settings/Audio/HMDI/Auto detect show as the detected audio modes?
And does this happen in a specific app? or all apps & the menu?