According to the screenshot attached to the tweet, it seems that the material needs to have oxygen atoms in exactly the right locations, too, not just copper. Annealing in an oxygen-deprived environment might not be conducive to that.

The original two papers were inconsistent with respect to the vacuum required in the process. Perhaps they were working with crappy equipment that can't maintain a vacuum and accidentally annealed their sample in normal atmosphere, giving rise to unusual properties. Kinda explains why even the original authors don't have enough good samples.