I understand what you mean about only 2 rooms in the category. But I think what
@scrappinginontario means is the same exact room wouldn’t show as available with both the BB rate & regular rack rate. They don’t list the actual same room in 2 different buckets. They would have 1 room listed as rack rate & the 2nd room as discounted. So if you booked the rack rate room, someone else might have booked the discounted room. Or there might be a glitch so it isn’t showing.
But if they did have only 1 room in that category available & strangely listed it in both buckets, you booking at rack rate just filled the category. So of course the discount went away, since there are no more rooms in that category available.
I don’t know when your trip is, you could wait & maybe the other room will become available & the discount might return. You could call & explain, see if guest services will honor the discount since you were unable to make the switch with your BB. If it’s really too expensive at rack rate, you could cancel & stalk the site to see if it goes back into the system as discounted.
Or just chalk it up to bad luck & keep the rack rate. Whatever you decide, I hope you have great trip.