The BT Box is relying on the Freeview service to deliver the channels you mention, so start by working through the troubleshooting there to make sure:
- Which channels you should get and
- If there is any works/issues relating to the transmitter serving your location
Freeview service checker: Which channels should I get?
Freeview service updates: Planned maintenance and transmitter information
Next steps are to check local weather as it can have an affect on Freeview signals: Bad weather help and/or BBC - Freeview reception problems
General question - have you lost these channels on other Freeview devices? Can you test?
If your TV is smart and has the YouTube app, you can watch many news channels including GB News live via that in the meantime.
Lastly, if all else has failed, it may be that you are receiving "too hot" a signal since the retune so the tuner in the box is slightly overwhelmed.
This is quite well known, search the forum for "Variable Attenuator" for instructions.
