so this happened with me and alduin, on the throat of the world, but never with harkon so this isn't a guarunteed fix. what i did was reload a save to before the fight happened and waited for alduin to aggro. do this with harkon and it may work.
i know this is an old thread, and i'm posting this just in case others look back on this for help.
I had a different issue revolving around the final battle with Harkon. Right before Harkon was about to die, my game crashed. I probably restarted the fight over a dozen times, all with the same affect. I'd completed the quest before on an old save, so I'm not exactly sure of what happened. I've started over on a new game, but I'm afraid to try again in case it happens again. What should I do?
is there something wrong with your pc/xbox or other console or is your game corrupted?
If playing with Mods active like some do, I have found by looking at everyone's problems that the installed/active mods are the problem.
I play Legendary Edition on both the Xbox 360 & my Laptop..
On both versions I've NEVER had a problem in killing Harkon & I used Auriel's bow every time on every play through.........
🤣🤣🤣 Love the "Try shouting" idea.... yes, screaming at inanimate  objects definitely doesn't work BUT it does help relieve one's own stress occasionally LMAO
I have the legendary edition and it’s happen to me also
I'm a console 0layer and what I did was killed home, he starts regaining health, quick save load the quick save