Judging by what you have said and my own experience it seems to me that this is mainly an automated response that is made worse by a Decision Maker who reads your file and does not have sufficient knowledge to make an informed decision. Then called for a Face To Face for no real need or justification.
It reeks of "Jobswortitis" and "Make a name for myself syndrome."
After all the horror stories I have read about these Face to Face interviews there is no need to worry if you get a sensible Health professional.
Got a new ESA letter dated 31/03/2017. Very strange letter listing all the rates of payment back from 2014. The payment breakdown sheet was for the 4th April 2014 to 10th April 2014. Why show 3 year old payments? Why not show the current one? No mention of the WCA that I attended and phoning them didn't help at all. Told to phone back later in April. Pension is now sorted and falls in line with the current payment dates. DLA is paid on top of my pension so I am a very happy bunny. As it looks at the moment there is no change to my payments regarding the WCA. So looking good