I did a run of the Sports Mix Category (submission coming in soon) and there is only one difficulty which is hard. Having Normal would not work for a sub category

Yeah, that's because of how SRC works, there are two options: Create the same subcategory 8 times (for each category that needs it) or asign it to all of them. The second option is better imo. It will be changed if it's possible at some point. I added a part to the rules regarding it.