Most of mine tend to be structural; realising that the operation my protagonist co-runs with the marines in chapter 9 can be used to introduce a couple of characters I thought she would not get to meet until the formal launch of the expedition in chapter 11, so I can restructure the plan for chapter 10 and 11 and I think they will flow more smoothly now is the most recent one of any substance. Also, I think I have seen how to do a frame story for this one if I decide I want to, which I am not yet sure about and probably won't be until I have written the whole thing linearly.