Do you check at 0:00:0x JST precisely at 360 days out? If you check even 30 seconds later (0:00:30), the J seats may be gone. I've experienced it first hand. Refreshed the search at 10:00:02 JST (back when it was 10:00 vs 0:00 release), got the flight, quickly rushed to purchase it, but it doesn't really hold it until third step (if booked using JL JMB), and by the time I got to it, as there was a mix-up with the credit card and I was literally boarding a train at the same time (at 10:01), the seats were gone as I was too slow to secure it timely.

If you watch it at release time, you will see that the 2 J seats are released, but may get snapped up within the first 30 seconds of when they are released at 360 days out. (And if not within first 30 seconds, within the first several hours in most other cases...and if it's an unpopular route/date, may be within the first day or few.) You cannot be tardy and need to move VERY fast to book it (have the CC info, pax info, etc. and everything pre-saved, so you can check-out and secure your flights in a matter of seconds). Also, sometimes if only 1 of 2 J seats is booked, the availability of the 2nd one is foregone and it disappears as well.