I've been having this issue since about a week before Lightfall launch. Despite the fact that I've had the Deep Explorer Boots unlocked as an ornament for my Warlock for a while now, they suddenly disappeared from my transmog menu roughly a week before Lightfall launched. I was hoping some of the patches rolling out would fix this, but haven't seen it mentioned under known issues. Relatively minor issue, but would really like some feedback and maybe an idea of when this might be fixed.