A new wrinkle...
The original PNR had 2 passengers on it, and one of them was my nominee. Status pass was already applied and one segment on the PNR was flown.
Had the PNR split so I could apply eUpgrades to my nominee. After the PNR split, everything still looked good in the AC app and under Manage My Bookings on aircanada.com - could see that Status Pass was applied.
On check-in for the last segment, only the passenger on the original PNR had the status pass and its privileges. The passenger in the new PNR, while in the app and online it shows status pass applied, didn't get the status pass privileges (no priority boarding or lounge notation on the boarding pass). Apparently, when the agent attempted to apply the status pass again, it comes back as unconfirmed. Couldn't apply another Status Pass either to the booking, system wasn't allowing it.
Moral of the story - don't split PNRs after a Status Pass has been applied.