Originally Posted by
PMFR
Had that in Nice, France recently. Has to do with you being "chosen" for Security Check. Your boarding pass probably will have "SSS" across the top left and you will be individually screened prior to being allowed to board. It is a random selection. There is nothing, other than a computer, that selects you.
While the check-in could be inhibited due to a SSSS hit, it could also be due to nothing more than a need for a manual document check prior to issuing boarding pass — perhaps even a boarding pass without a haraSSSSment flagging — and the airline getting a feedback ok’ing the passenger to travel. Or it could be other things that are even more minor on average — say seat assignment issues or things sort of like that.
Some SSSS hits and other self-check-in inhibition is rather manually-based and is not just by automated computer selection.