My guess would be the install versus Save location, since you've done a Windows OS upgrade. While there are no overtly "cosmetic" differences in the basic functioning of the OS, there are some internal differences, and I would first experiment with a "clean" Save folder, but you wouldn't have to necessarily empty it, just temporarily move it elsewhere to where the game can't find it. Then do that same Single Mission. If it still does the same, you will most likely have to re-install the game and start a-fresh... You might also find other apps from your Win7 install that will treat you the same, acting like they are functioning as intended, but not really doing so... Hopefully it won't be any of your important apps that do that... But anything "legacy" (as far as Win10 is concerned) is suspect.
