Yep got this bug on all my boxes (4K and puck) that have the crap 'new' software on! 🙄
The Freeview Smart box that still has the old software doesn't have the issue, just like it never had the unknown page error issue either. Go figure!
I'm having same problem this evening and have had system for a few years. 1/4 quadrant - the upper left one is translucent but greyer than the other 3 quadrants and the border lines are quite marked. Some kind of overall problem with the network this evening? (It appears no matter which channel I view)