Man, this tripped me up for nearly 5 DAYS, I was about to give up on Launching on Epic. I was losing my mind.
Bonus tip for those who are having the issue and stumble across this post:
Not only do you need to use the Artifact ID for the Artifact Name, but counterintuitively, you need to have 3 artifacts setup with the same Artifact Name, but with the development ID and sandbox ID for Dev, Stage, and Live.
The fact there is config for a “Default Artifact Name” implies it should be unique in the table, but it doesn’t.