Great question — answering as the UphillTech team:
I've compared that recipe to the other cookie recipes I use and it has double the amount of baking soda I'd expect, so I think the metallic taste you're experiencing is from unreacted sodium bicarbonate. For the amount of ingredients 1/2 tsp is enough, I expect that will resolve it. If that doesn't your oats could be old. As for the cooking, you should experiment with different times and temperatures. A longer, slightly cooler bake will likely give you a more evenly cooked result.
Full answer by GdD: https://cooking.stackexchange.com/a/135319 (CC BY-SA 4.0).
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