My iPad 10 on iOS 12.0.1 locked up when opening an html file from Dropbox. Flashing sign: “Leaving Dropbox This file is trying to open another app. CANCEL CONTINUE.” Cancel or continue buttons are not functioning. I can’t clear this. I’ve tried tapping, closing and rebooting both Dropbox and the iPad but none of them clears this error. I also tried to update the iOS software.