Same here. Neither Ä or # is possible. And you have to do restart the machine that the new shortcut will be accepted.
Further... aufofill still doesn't work at all. I still get the popup window and i have to click the item to get the login. Frustrating...
It's working but only with a German keyboard with numeric keypad (see screenshot). On a MacBook... no chance... very frustrating that it's not possible to set a custom shortcut for this. I just switched from 1Pass and I'm getting to regret it...