Answering the first question - yes.
It mostly happens when I find myself facing a crossroad, when I have two ideas on how to solve a conflict/push the story forward, but I have to pick only one. It's so hard to choose when both are equally good, just from a different approach that doesn't have a crucial impact on the further chapters - either character A handles the situation like a badass, or character B handles it in their own unique way, etc.
So I have to pick one and ditch the other.
That's why I plan to make my stories into choose your own adventure stories or Visual Novels one day. I can keep both ideas, and let the reader decide which one they like more X3
As for the second, it happens too. I totally forget parts of the dialogue... and it pisses me off, because in the back of my head I remember it was perfect. I get the angrier when I can't find the notes with the important conversation in, and I have to either remember it again or come up with something else (but I don't like the new idea as much).