Tried Ethernet with no change, these BT TV Pro boxes are a complete joke what are full of flaws, I get why people stick with Sky, even TalkTalk has dropped these boxes
Assuming you're in contract, BT will replace it if you report it as faulty
The Now channels through the app will always look sharper as they stream in HD as standard, (just to be clear not Full HD). While, without the HD add on, through the YouView box they are SD only.
In fairness the BT Pro box is s great bit of kit and the HD quality is sharp.
You need to confirm, do you have the HD package?
If yes are you actually tuning in to the Sky News HD channel and not the SD one. There are two SD options one via Freeview and the other via the Now SD channel on the EPG.
As I have stated previously if you do have the HD subscription then select Sky New HD channel 385, the picture quality should be sharp, if it isn't then you do have a problem.