That drop is a real puzzle,
@emily deacon . Don't know how long you've been dx'd but one thing to think about, if only to rule it out, is lipohypertrophy. If we've been dx'd for a while and inject in the same area too much, some subtle bumps can build up and they really mess up the rate at which insulin is absorbed. It can sit there for a while not doing anything then fights its way past the lipo bump and gets to work at unexpected times, hence unexpected drops. Lipo bumps can feel like a bit of firm avocado just under the surface, so maybe worth having a look at your injection sites.
Of course, it might also just be that when you injected at 10, presumably as a correction, insulin takes a while to fight past high levels, but, once it's done so, if there's still a fair amount of it left on board, there can still be some pretty harsh drops in the last couple of hours of action.