I wonder if through the writing process your characters have changed what you originally intended and now need/demand a different ending? Maybe the ending doesn’t fit anymore and you’re trying to force them into a situation. Possibly? Or maybe what you need is time to just sit back and let it simmer for a bit. Re-read through the chapters leading up. See if this is the natural progression. If it is, then it will come to you. If not then your characters will lead you to the right ending for them. Fingers crossed for you… I hate when I get stuck and don’t know where to go!