Ive recently been getting this error - the box was working perfectly for around 6 months a has now just decided to stop. Multiple resets and retunes later still absolutely no luck 😢 happens on most mainstream channels like ITV, Channel 4 & Channel 5
Ariel tunes perfectly directly into tv with 0 issues!
There's a few suggestions on the web (including BT's Robbie's post of 2018):
Assuming that the BT channels are ok and the problem is with the Freeview channels alone, plug the aerial into the BT box and check for free play in the connector. If it seems loose then the aerial socket is faulty and you need a replacement box