Gareth
If your friend has been in the WRAG since 2015 then their ESA(CB) will have been time limited and will no longer be in payment. Although they technically still have a claim for ESA, the DWP will have deleted their computer records.
Being placed in the Support Group means that their ESA(CB) will now go back into payment, but this cannot happen until a new computer record is built and this is why the ESA1 has been sent.
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems