I'll see what happens first. Over the last year or so, I've only used it for recording (not viewing), as a fallback for when Freesat doesn't record, since Freeview gives such a poor selection in our area. However, my Humax Foxsat-HDR broke down today, so I went to Freeview and discovered this problem, dating from about 9 days ago. I see no reason why it should suddenly start failing to record unless something else outside the house has changed.
If the problem comes back after rescanning today, I'll do as Martin suggests, but my first priority is getting Freesat working again.
Thanks for the help