I suspect the challenge isn’t working for a lot of factors actually. Looking at the requirements to start the challenge vs the changes to the coreset, it is likely the challenge required:
- Core Murloc Tinyfin
- Core Acidic Swamp Ooze
- Core Mossy Horror
- Core Krag’wa, the Frog
All of which left the Core set with rotation. So check all of them to see if they are instead pulling in the non-core versions from your various wild sets like Rastakhan and Witchwood.