Just read elsewhere... that's not it.
The US only approved for X number of flights and they did not approve for a flight from Amberley, the Sat demo and Sun demo and reposition to Amberley. Therefore the Sunday demo had to be cut to allow for the Monday reposition flight as it would have departed on Sunday after the airshow demo, but it couldn't due weather.
That makes sense. It's likely to do with cycles and maintenance - an extra flight now could have flow-on impacts for training flights later. There are only 10 of these things flying apparently.