At High Wall of Lothric in Dark Souls 3 you encounter a dragon (Lothric Wyvern). At least that was a case for me at the begining of the game.
I collected all loot near it, but I never touched the dragon (I am sure of this, because I have no idea how to lure it out and fight it with a sword and I don't use bows and magic). Then, at the end of the playthrough I decided to visit the dragon and try to kill it. But there was no dragon… Where, when and why did it go?
P.S. I wonder if this is the one, which comes from the sky to Lothric Castle bridge.
Best Answer
Well first off,
If you wanted to kill it you couldn't. If you do enough damage to it (when you have it on High Wall of Lothric) it will simply fly away leaving a Large Titanite Shard behind.
To me the same thing happened. I went through the game and by curiosity I came back and the Wyvern was gone.
I revisited in 2 points of my game. One of them I saw the Wyvern again and the other no.
One thing that I'm assuming is that it can be a bug that the developers overlooked. Or it might be that one of the Wyverns at Lothric Castle is the same at High Wall. Since I killed it, the Wyvern disappeared.
EDIT Like @fhlamarche said in the comments below, he made a new character and instead of going to other areas, he went straight for the Dancer of the Boreal Valley and then to Lothric Castle (to the bridge).
There were the 2 Wyverns and when he came back to the High Wall there was no Wyvern to be seen.
Coupling the experiment with the fact that in the High Wall you can't kill the Wyvern (Like I said previously, it just flies away) it seems that the High Wall Wyvern IS one of the Lothric Castle Bridge Wyverns.