This could well be the TV has failed to detect the initial sound.
Most TV’s if not all current, are designed to support multiple European country standards and encoding standards.
You could try varying the power-up options e.g. Humax first, TV later or the reverse.
One thought, if you power-up as current practice and the change the picture resolution does the sound now come on? What sound setting is active : Stereo or Multichannel, if multichannel try a change to stereo.
I have presumed your TV normally provides the sound.