Comments like this are off the wall, incorrect and obviously not helpful to person worried about the patdown.

I have been unable to do on-line checkin only ONCE due to SSSS. I have been unable to do OLCI numerous times for other reasons -- too many segments, need to verify passport, mangled flight # on a codeshare, DL resv. flagged my PNR so agent could ask if I wanted a more direct routing, UA botched a booking on US & it ended up as a paper ticket, etc.

Yes, it can be SSSS. But there's more likely some other little detail that somebody or some computer think needs attention.

These days there is often no patdown with SSSS. The last time it happened (rebooked at the ticket counter after flight cancellation) they were more interesting in swabbing my mutliple computers & other toys than anything else.