There was an update at midnight on 13th November, and TVs all have to be retuned for that. I think it has something to do with 5G, but that may be wrong.
Anyway, it's nothing difficult, you just retune your TV, and if you have a set-top box or PVR such as a Humax, you retune that.
When I did it, a couple of channels had disappeared, but they came back when I did it again. I also lost a couple of things I had set to record (BBC4 very late/after midnight) as the signal must have gone by that time. All is well now, though.