Problems Combining Datapacks

Im trying to combine two datapack, one I have made myself and made by someone else (I have permission to combine them). The datapack made by someone else works on its own, but when I combine it or when I put both datapacks together in a world, it stops working. To be more specific it is very inconsistant when working (ie. it works sometimes and other times it doesn't). I need advice on how I would go about solving this problem.