The channels you're missing are all on the PSB2 multiplex ( = 'bundle of channels"). Each multiplex uses a different frequency. In theory you should have a different aerial for each multiplex (so that the elements are exactly the right length to 'resonate' with the relevant frequency). In practice though we all use just a single aerial, which is bound (by the laws of physics) to be better at 'resonating' with some frequencies than with others. Your aerial clearly doesn't resonate well with the frequency that's being used by PSB2.
Either PSB2 has migrated from a frequency that your aerial 'likes' to one that it doesn't or the power level used to transmit PSB2 has been reduced. (A lot of the retuning that's been necessary with Freeview services is related to the rollout of 5G mobile phone services which, as well as involving frequency changes for Freeview, has also required a significant reduction of the power used by some Freeview's transmitters in order to avoid interference to 5G services).
Either way, the problem you're now facing is one of insufficient signal strength for the combined needs of your aerial and your TV. You
might need a new aerial installed but it's far more likely that you can solve the problem simply by installing one of these:
https://www.argos.co.uk/product/9383027
(You'll also need one of these to go with it
https://www.screwfix.com/p/fly-lead-coaxial-plug-to-plug-1m/41720 and you should carry out another retune after fitting them).