Lip sync issues

I’m in the UK and I purchased my Apple TV 4K around 6 weeks ago and have had lip sync issues from day one.

I subscribe to Now TV and when I watch sport in UHD through my Apple box that’s where the problem is. The audio comes out before the lips start moving. If I watch the same content in HD through my Apple box it’s absolutely fine.

If I watch the same content in UHD through the Now TV app on my TV it’s absolutely fine, so the problem must lie with the UHD content coming from the Apple box.

I have had telephone conversations with Apple support going through a few troubleshooting steps, the last one being a full factory reset which didn’t resolve it either.

If anyone has had similar issues and solved it or can offer anything else to try I would welcome your input.