I went through SAN on Thursday on the 273.
No queues at all - in fact couldn’t spot any other passengers from any other flight.
I went HBO - and got the Spanish Inquisition from the CBP guy. And I’m Global Entry - used to waltzing through. Got quizzed on everything about my trip, had to produce return tickets, proof of Global Entry - like the good old days of US immigration. Not sure if they’re extra cautious at SAN, if this was a one off, or I just looked extra dodgy.