I took a break from WOW during dragonflight. When I logged in for the 20th anniversary, I noticed a number of my mounts are missing. The ones I can identify for sure are the Jade, Sapphire, and Ruby panther mounts that I made on my jewelcrafter during Pandaria. I noticed them when trying to compete in the Mount Mania event and could not call up the panther mount that I was supposed to have. I am not sure what other mounts may be missing yet.
I have talked to a game master person. I have followed all the online help that was offered.