After registration and login in on multiple devices, you may encounter this error. When logging in on a device, you will be asked if you want the list stored locally on the device to be associated with your account. If this is affirmed, it can happen that on both devices the new (probably empty) list is selected as default list. The list must then be changed back to the old list, or the new (empty) list must be deleted. This can be done via the list element in the side menu under the profile.