Originally Posted by FlyerBeek

As someone who flies longhaul internationally monthly, I receive SSSS on about 50% of my international return segments, despite having a TTN, GE, and a reliable and consistent history of frequent travel. It's a fact of life, nothing more nothing less.

Given the OP's origination in LIS, presumably he/she had a BA-issued BP for the AA flight that did not indicate SSSS (making the OP think it was the FL agent who added the SSSS). It is completely common to have SSSS appear when the boarding pass is reprinted on AA stock. I had the exact thing happen to me last month returning from Europe. If the OP had attempted to board using his BA-issued BP, he would have received the exact same secondary screening at the gate. The FL lounge agent had nothing to do with this.

-FlyerBeek