Why do I get a message saying “This account is in use on another device”?
You can be logged into only ONE device at a time. If you log into another device, the previous device will be deactivated whenever the app tries to backup to the cloud or does a status check (about every 15 minutes). Unfortunately, that means that any work you did on the previous device since the last cloud backup will be lost.
If you want to switch devices, you must FIRST log out of the one you’re using (use the More menu on the bottom bar), and THEN log into the new device. You will need to be connected to the internet so the previous device can backup your data and the new device can download it.