My RAF, Dragonflight, and a few covenant transmogs are compeletly gone, as are the associated mounts.
First, check all your filters in the each journal (mount & appearance). I have noticed the filters keep turning off for some reason.
Also, the issue with account-bound transmogs (such as RaF or from Shop) that Blizzard thought they had corrected has still been happening.
They are aware of the issue with the transmogs and are working on correcting it.