If a note is close to the bottom of the screen and you press the date icon to bring up the date dialogue box, the box can come up with the bottom disappearing “off the bottom of the screen” so that there is no way to see, or press the “Assign date” button, and because the button is not a standard default button you can’t press “return” to activate it either.
I am running Beta 7.0 on iOS 13 public beta, iPad Pro 12.9”, but this behaviour was also the case when I was running 6.01 on iOS 13.