i have been ssss a few times. I have tried to discern if there is a pattern to when I get it. Once I was very tight on my check in f(at that time 45 min. prior to departure was the stated policy, i was right at one hour trying to check bags curbside. I don't know whether that prompted of if I was randomly selected regardless) the other times have been when I have tried to check in and opt for a standby before going through security rather than at the gate. Not sure whether it was the standby or not. One standby, was a flight out of sfo that I was late for. I arrived at the ticket counter check in, prior to the flight but too late to effectively make it to the gate. they gave me a 'standby' boarding pass rather than a boarding pass for my actualy flight. it was ssss. my wife also got the same thing which suggested to me that it had to do with the standby nature not anything else.