I’ve run into the same problem. I went back to the first Grounded game to get the new Achievements out of excitement for the new game and found out that this challenge was bugged. Kinda put a damper on my personal hype.
I finished all of the other challenges thinking that maybe it would think it’s complete once I finished everything else and the achievement might still unlock. No luck. Tried resetting the game and Xbox as well. Really wanted to finish this before NG+ and don’t want to look for all the Milk Molars again. I guess I’m done for now until a patch is released.
