Cathay Pacific Bookings

Hi everyone, I'm new to travel redemption, so please forgive me if I'm missing something obvious. My friend and I are trying to book for Japan for April-May, and I've been checking flights throughout the day on Cathay Pacific for AA. I keep noticing that flight availability on Cathay Pacific seems to change constantly. I don't think the seats I'm looking for are sold out but I'll see a flight available at one point, then an hour later it disappears only for it to reappear again later. Sometimes the same flight shows up but only in premium economy or first class or only as a one way option. I'll check on the flight again later and it'll be gone again. Is this expected or is something else going on that I'm not aware of? I just want to make sure before I transfer my points and be unable to transfer them back. Thank you!