Same for me today. And I've definitely had it before. I don't have SFO-YVR, but I do have YVR-YYZ. Extremely frustrating, because for a 0700 flight, I just want to get out of the car around 0630 and walk straight to security.

However, if I use my laptop to go through the check-in flow, it very clearly says "Your reservation requires additional verification. Please validate your documents at an airport kiosk or with an agent to receive your boarding pass(es)."

Extremely frustrating, since in days of yore, you could get a BP and just do a doc check at the gate. Now I have to spend an extra 5 minutes going to the check-in counter (I doubt the kiosk will work after check-in closes) and making the walk to security, rather than just getting dropped off at security.