I had a problem with the hotkeys not saving and tried several methods. I did find a way without changing any files and wanted to share this since it was a pain for me.
Solution:
When you want to close the game or save the newly assigned hotkeys, make sure you go to character selection first and then close the game from there. From what I understood, closing the game directly wont save the hotkeys and will lead to default or last saved hotkeys.
