There is an apparent bug in Season of Discovery when on the quest “Warranty Claim” (https://www.wowhead.com/classic/quest=79982/warranty-claim).
When you kill a mob and the Shadowy Figure spawns there is a chance you cannot see it.
I was solo farming in Desolace for about 2 hours and could not get it to spawn. Then a few people invited me to their group. We were farming for about 10 minutes, just killed a mob and I moved onto the next one. They told me to come back. When I came back over there was nothing there. One guy told me to relog as a similar thing happened to his friend.
I relogged and sure enough there was the figure.
So for those 2 hours I was by myself I can only imagine the Shadowy Figure appeared for me many times but I just couldn’t see it and didn’t relog.