3 month wait for LCWRA element?

Client is receiving UC and was assessed as having LCW with effect from September 2021.

If he now notifies a change of circumstances relating to his health and is found to have LCWRA, will he have to wait for a further three months before getting the LCWRA element, or does Reg 28(2)(b) mean that it should be added straight away?

Yes. See para F5046 here.

Because opening post contains two questions and for the avoidance of doubt
No - a relevant period does not have to be served, and
Yes - the LCWRA should be applied from the AP in which the change was reported