When the defenders were rushed they might create a line in which they could not clear the timber and brush in front of the line. That may have happened at Spotsylvania. At Vicksburg, I believe one of tactical commanders found an uncovered draw, and his regiment made up to and over the parapet.The thing is, though, the tricky bit is getting over the "last hundred yards" - and you'd have to be quite blasé to accept a defensive position with a covered approach to it. Certainly some defenders made that mistake, but others did not.
Meanwhile close terrain also impedes the ability of marchers.
I'd feel somewhat more confident that war had changed from the Napoleonic period if what you actually saw during the war was Napoleonic tactics being tried and failing. But there's no appearance of the ordre mixte, attack columns generally do not appear (and when something like them does they usually work)...
But the Confederates had many good military engineers and they knew the angles and fields of fire they wanted to defend.