That's a little disconcerting when you're looking up a coin you hold in your hands. Given the propensity of PCGS' varying information sites to go up and down like an ocean buoy in a storm - I can only use PCGS Pops about half the time - it might be worth waiting overnight, rechecking tomorrow, and contacting them if you still get a bad result. I wonder if someone disconnected that cert from their own Registry, and instead of just removing it from the Registry they removed it completely by accident?
Yeah, I would just call PCGS tomorrow if it's still an issue, and assuming you're confident the coin and slab are legit.