I'm trying to book YYZ-JNB with a stopover in FRA on the outbound. Found a great itinerary and price on Matrix, both legs are AC fares so I figure I should be able to book with AC to get my SQD.

I tried initially to book on AC.com, I can select the YYZ-FRA leg, but then it says "no flights available" for the FRA-JNB leg even though of course there are. I figured this was an IT problem, so I called reservations and tried to spoonfeed the itinerary. However, the agent said he couldn't book it because a) there was a stopover and b) the second flight wasn't AC. (It's LH of course.) The fare rules do allow for stopovers.

My inclination is to HUCA. However, my one hesitation is that I can't actually replicate the Matrix price anywhere else (Google Flights, Expedia, etc.) so maybe it actually isn't bookable. Is there such a thing as "phantom availability" on Matrix?