Upgrade certs not honored at airport… but seats were still for sale?

Trying to figure out what happened here.

Called reservations about two weeks ago and used two upgrade certificates for an international flight. They confirmed the request on the phone.

At the airport, the desk said they couldn’t see the upgrade request at all and told me first class was sold out. But when I checked online, it was still showing two seats available for purchase. Later, they ended up putting two standby passengers into first.

So now I’m confused. If reservations could see the upgrade, why couldn’t the airport? And how did standby clear into those seats if they were supposedly sold out?

Has anyone run into something like this with Hawaiian?