2020/03/10
From Android Q onwards, Google have blocked apps from accessing the public documents directory, which is where Kanji Tree Pro used to store the user lists.
If you upgraded your phone to Android Q, and subsequently lost all your user lists, this is why. They will still be on your phone somewhere, but unfortunately Kanji Tree can't see them any more.
If you want to restore them, you can do so either by connecting your phone to a PC, or by installing a File Manager app on your phone.
More details to follow...