A quick fix which almost always works is to press the record button and start recording a TV programme.
Wait a few moments and go back to the recordings and you can usually see them.
Thanks, I did try this at time. Recorded live TV for a minute or so. The recorded programme appeared in the recordings list but it didn't bring anything else back until I restarted the box.
If it doesn't work the first time, wait a few seconds and try again - it almost always works then.