If you find a friend with a milling machine, you may be able to save that latch by machining about 1/64" off the bottom surface of the latch. It will have the effect of sharpening the rounded corner and make the latch sit down flat again. Flatness is paramount so i would not chose to do it with hand tools. Too easy to put a curve in it.
I had intentionally rounded mine to make them easier to open, which worked, but I went too far on one cap, and it stuck upwards like you describe. The machining above will fix it.
Of course, when you reassemble, the bottom disk will need to go onto the stem a partial turn further before locknutting.