I love TBIT, but I had a remote stand on Friday 7 July.
The bus departs from the remains of the old TBIT, which is a zoo. And of course they have no way to separate the status or Business Premier or even Premium Economy passengers.
So they don't call the flight in the lounge until all the Economy passengers at the (bus) gate have boarded. The pointy end and elite status passengers then feel as if they are boarding together, and aren't intended to notice that everyone else is already on board!