Head to the western part of the zone, find the plateau where only one "a burly hill giant" is roaming amongst 8-10 leopards, this is the right spot.
Now look for the single mob which is out of place, it can be the following PH's:
a dire wolf
a hill giant
A stone viper
A brown bear
I kept killing the burly hill giant and these PH's for days with no luck, so decided to kill everything on the plateau, and don't know if it was blind luck, but after the second respawn, Oldbones showed up, but none of the above PH's were spawned, and the burly hill giant was also up, along with all the leopards.
Respawn time was not static, was between 17-21 minutes for the entire plateau.
I also had Midnight spawn on the plateau as well, after the first full clearing of the leopards.