Unfortunately you have been bit by a series of Android Bugs which started with 4.1 but still affect
users with even Android 4.4.2. which causes FocusGTD accounts (to be more precise accounts of all
paid apps) to be removed during app upgrade and phone reboot.
The details to these bugs are listed here:
Therefore, I have created an app that will work around this issue:
Info for Samsung users: at present you’ll need this app too, see
The bug causes accounts of paid apps to be removed when Android boots up
(or when you upgrade the currently installed version).
To work around this issue this app pretends to provide the same account type that FocusGTD provides.
This is enough to convince Android to keep the account.