On 7/4, I was flying CTU-NRT on NH, switching to NRT-LAX on UA. I attempted to check-in on-line in Chengdu, only to no avail (the NH app kept on erroring out). When I checked in at the airport, my first BP (CTU-NRT) was fine, but the NRT-LAX had the SSSS. Even when I got to NRT, I attempted to OLCI on the UA app, but it gave me my traveling partner's BP, but mine was replaced with "this is not a boarding pass." At the gate though, they made me take off my shoes (sandals) and swab them, and let me go on my way.
Now, last year, I was flying MNL-HND (also on NH), followed by HND-SFO-LAX on UA and I had attempted to OLCI via NH, and on the HND-SFO I got the SSSS (so I had to re-print my BP at SFO, which showed PreCheck). Yet, earlier this year, I flew MNL-NRT (on NH) followed by NRT-LAX (on UA) and I didn't get the SSSS; but then again, I didn't try to OLCI either.
Could the SSSS be related to my attempts to OLCI via NH?