Thank you for the detailed review. I’d noticed the hotel has swapped between Autograph and unbranded a couple of times since it has been available on the Marriott site (seems to be Autograph now); I can’t see how that impacts breakfast but sounds like you got better in the end than I had at the Saint, albeit with a lot of discussion.
You do wonder how the customer facing side of the hotel can be so inconsistent - there should be procedures set up for everything and staff trained accordingly. All of this could have been done while the building works were ongoing so there really isn’t an excuse for what you experienced.