J class redemption seats release
 

I've been seeing one J class seat pop up for a flight on Cathay pacific redemption, disappears for a while (hours to a few days), then pops up again. Are these individual seats being released every time? I'm trying to redeem 2 J class seats

These seats are removed from availability, once you enter the payment stage of the ticketing. The payment stage can be just a couple of minutes, or, when something fails with the payment (or the customer just disappeared), a max of maybe 1-2 hours. After that, the claimed availability being processed for payment is returned to the general availability. This may be, what you see happening.