This always happens to me. I start a story. I have the ending plotted, I know my characters and world. The middle usually ends up a haze for me till I've written the beginning and then started to plot my way backwards. But somewhere in the middle something happens that stops me dead. With Spandex it was finding out that Maisie would work better as Matt. I discovered that plot twist somewhere in the second third of the first draft. In that case I ignored the first part of the novel and wrote the last of it as if Maisie was male. Then I edited, and edited, and edited.
Wren's song stopped me early and although it's demanding a new beginning, the change isn't nearly as drastic. I've dumped some scenes, put a few in a file to see if they fit in later, and rewritten the first 2k to line up mostly with my middle. I've got about 8K of words to edit tomorrow and then most of it should be able to fit in. I'm hoping to unoffically Nanowrimo this story, which should put me at about 60k coming into the Dec. That should put me at about 3/4ths of the way through the text. That is a happy point to be. Since I'm not ditching everything I have to start fresh on Nov 1 I am not joining any of the official things but I'm hoping it will be fun and press my word counts to a new height.