I'm run into a really odd bug. The Griffon that you have to rescue for Uthar Griffonsteel hasn't spawned or if it did the undead killed it beofre I could go free him.

I know where the Griffon is meant to be but it's just not there and I'm cleared the map as well. I'm stuck and can't complete the map.

He is there, you just havnt seen him, just below the hero monument is a small trail going up/north.
You can take away the fog by pressing Ctrl + ] to open console,
then type in field
UnExplored:Enable (0)
take note on the Capital letters in that command,
then press Return to execute the command,
then press Esc to take away the console