I've had it happen to me a lot as well, and I know it was discussed in the discord but I don't remember what everyone thought the cause was.
Fixed. Thanks for letting us know.
We made 100% just Easy, Normal, and Hard mostly because the Hero missions would take a long time on top of a already very long run. We also have what we call True Hundo, which is 100% except with Hero mode as well, although it's mostly a meme since no one has run it. Hope that answers your question.
Yeah they have DLC allowed in the rules for both NG and NG+, so you're good.
Basically you can do them in any order that you would be able to in Legend mode.
You can't really reset the maps in Hyrule Warriors for runs, the maps are just linear enough that it's easy to tell which levels unlock others, so we just start with the first mission and go in a line through the ones that get unlocked.
Well it's obviously different enough to not put co-op runs in the same category, but I guess it depends on how the individual levels in the adventure modes work. Like if there's any levels that are already played that could be sequence-broken or if there's some different path of levels on the map screen that are faster to complete with two people than the current ones played.
When you're at full health, the Master Sword has additional beams on the C2, C3, and C4 combos, giving the attacks much more aoe enemy clearing and single-target dps. The strong attack and C4 are also much better on the Master Sword. If you were hurt, it might be faster to have a hasty Hylian Sword, but with as many heart drops and potions that there are, it isn't too hard to keep the beams. Hope this helps :)