As part of the 700 MHz clearance programme (to free up frequencies for use by 5G mobile services), changes were made to transmissions from the Emley Moor transmitter (that serves Sheffield) on 23 October. Your aerial could handle the old signals but it's now very borderline when trying to 'pull in' the newer ones. (That's partly due to frequency changes but it's also possible that the power output from the transmitter was reduced at the same time in order to avoid interference to 5G services). So it can 'pull in' the Freeview signals when conditions are good but a slight change in atmospheric pressure, a solar flare on the Sun's surface or interference from your neighbour's microwave oven or printer could be enough to render the signals unusable to your aerial.
You
might need a new aerial but most people in your situation find that installing one of these
https://www.argos.co.uk/product/9383027
and then carrying out a retune is all that's needed to cure the problem.
(You'll also need one of these:
https://www.screwfix.com/p/fly-lead-coaxial-plug-to-plug-1m/41720 )