Seems specific to my situation: the clinic where I got my 1st dose never submitted a claim to UHC, so they don't have a "verified" record of it. The web page lets you self-report by uploading the CDC card, but the QR code that is generated only encodes the 2nd dose (which they were able to verify via a medical claim). So when verifying the health pass I show up as "partially vaccinated". But I did scan the code with the smart health verify app and it looks to be a valid format, so for others who use United Healthcare in the US this might be a good option.