I’ve noticed this with actual things I have form the shop (the fire horns helmet) as well as other mogs in a somewhat similar vein, namely the explorer’s outfit from Recruit a Friend. I will pay to mog the outfit and it may persist through a few logouts but eventually it will wipe to my standard gear appearances and I have to re-mog it.
This has been going on for a long time, several months at least, but I’ve noticed recently that it doesn’t happen with my Vestments of the Eternal Traveler and I’m not sure why. First, I want to report this bug so hopefully it gets fixed but I’m also hoping some players know some way to get the mog to “stick” properly.
It is a very known and very well-documented bug. They are working on it, as they have been since it first broke in June with the release of 9.1. There is currently no fixes or work-arounds.
You have the mogs that you paid for. Unfortunately they disappear from being mog-able with no rhyme or reason, just as they’ll reappear the same way.
You are welcome to request a refund for the Celestial mog, but that’s kind of it at this point until they figure out why this is happening to some people, but not all - and why it’s happening some of the time but not all of the time.