Those channels are transmitted on the PSB2 multiplex, which has changed its frequency.
Theoretically you need a different TV aerial for each frequency that you want to receive, so that the lengths of the elements are a perfect match for that frequency (providing optimal 'resonance'). That's clearly not possible so we all use a single aerial which will be better at 'resonating' with some frequencies than with others. Your aerial was well-matched to the old frequency used by PSB2 but not to the new one, meaning that it's not up to the job of receiving those stations which are transmitted on that multiplex.
One of these should fix the problem for you:
https://www.argos.co.uk/product/5713543
You'll also need one of these to go between the signal booster and your TV:
https://www.screwfix.com/p/fly-lead-coaxial-plug-to-plug-1m/41720
(You'll need another retune after you've installed the booster).