The power industry has been struggling lately due to the unseasonal hot weather and air con. The power plants try to work out when is the best time to do essential maintenance with the smallest loss in profits . September has back fired on them and high prices have been paid by the grid for electric , obviously the grid does not like high prices and frequency control is used to aliviate problems I would suggest the frequency was down on the night of your gig and no other problem exists.
Keith