For the first time in my life, I got SSSS on my boarding pass. Is it normal to get it on the inbound rather than the outbound? When leaving the US, everything was normal. I was able to get my digital boarding pass from the UA app as well.

I was thoroughly searched. Everything in my carry-on was taken out for inspection. They were also swabbed for explosives. I had a pat down as well. The whole process took about 10 minutes. I'm still on the US-bound flight as I type this post. I don't have any checked bags, can I expect another search when I arrive at SFO or more scrutiny from CBP?

Since I have a long layover at SFO, I wasn't able to get the boarding pass for the other segments. When I do eventually get them at SFO, will they have SSSS on them since the first segment on the return trip have it?

I'm not able to get the digital boarding pass. Is this related to SSSS? Since I passed the search, will the UA app eventually display it? Or it won't give any digital boarding passes for the remainder of my trip?

Is SSSS only for US-bound and domestic flights? I'm assuming this doesn't exist on an LHR-CDG flight?

Is this a one-off or I can expect more SSSS in the future? If I get it again, should I write to DHS?

TIA!