Stellar 55 sound problems.

Max

Hi,
I am having some problems with the sound on my new Stellar 55.
After streaming content through, say, Netflix, for an hour or so, if I then switch back to live TV I get the live TV picture, but no sound.
I can go back to any of the streaming services and get picture and sound, but if I go back to live TV all I get is pictures only.
If I stream content for a shorter period of time it doesn't seem to happen.
The only thing that seems to fix it is to turn the TV off completely at the power socket and then re-start it.
(A very similar thing used to happen with the Bild 7 the new TV has replaced - after watching streamed content for an hour or more through an Amazon Firestick, there would often be no sound if you tired to return to live TV).

Any ideas?

Kind regards, Max.