Just checked on the Now app on our 2020 LG GX, running over WiFi, and with Boost.
The Good Life was showing.
It pixelated for a second, but then locked on and was fine, or as fine as an SD 4:3 programme can be.
I tried some other live channels, and most came straight up, but 3 had initial pixelation, even including Sky News.
So nothing unique to UK Gold.
Have you tried powering down your router, right off at the mains, waiting two minutes, and then powering it up again?
Followed by doing the same on your TV?
Worth a try to see if that fixes it.
Humour us. Sometimes streaming services will start working properly again after a router power down.
Something I often do to keep the stream consistent.
What about unplugging the TV?
You could try clearing the cache.
Worst case you can set it back to factory settings.