The Algarian Stormrider from the pre-order disappeared from my mount journal after I logged in today. The button for it is still clickable but says You have no valid mounts when i press it.
Edit: I also have the same issue as others below, also missing the transmog set.
Edit Pt 2: As of 4:38 EST, I now have both the transmog set and mount back in my inventory
I have the same issue.
Same issue here as well. Also my character suddenly shows no more armor (despite having it equipped). Seems there are a quite a few bugs flying around since today
Same, I logged in naked, pre order transmog set is gone and so are ALL my dragonriding mounts on every character. Can’t fly anymore
Same here the mount is gone and so is the transmog set
Same… pre-ordered the epic edition, logged in to find that everything had been removed. The mount, the FoS for having the mount, both of the armor sets, the title for doing the races, the hearthstone, the pet… all missing.
Having the same issue here. The same thing happened yesterday with the Gleaming Moonbeast.
Same issue, looks like everything tied to the pre order is gone. Boost, transmog, toys and mount.
The bnet launcher lists my account as War Within, but Blizzards account site lists it as Dragonflight
Same - logged in. Toon had been in the storm set, now naked. Mount and all toys and such gone from inventory. They don’t even show in the “not collected” pages of the areas they should be in.
Same, all of my pre-order stuff (that I’ve been using for a couple days) is suddenly gone. The Algarian Stormrider mount has disappeared and is no longer listed in my mounts, missing the transmog set, etc.
Same for my husband, who just logged in to check as well. All missing.
We both have Heroic preorders, in case that is relevant info.
same here. Algarian Stormrider Mount is missing from my collection along with the mog.
Here as well. And I splurged for the Epic edition. Everything from it gone. EVERY. THING. Boost, Tmog, Pet, Mount, even the title I EARNED. What the hell Blizz?
also missing all my pre-order stuff 
Same issue.
Same issues.
yup same issue
Ok well just now the hearthstone toy came back. And I can now see the gryphon again on the mount page, but it says uncollected (even though it looks exactly how I customized it prior to disappearing on the mount preview page)
Same issue here. Pre-ordered Epic edition. It’s all missing… Mount, transmogs etc.
Take back some of what I said. Relogged and got my Title back at least but don’t have the mount or anything else. Just the Title
Had the same issue. Closed the game and relaunched and everything showed back up