This may be related to our anti-cheat mechanism^^
We have an anti-cheat mechanism in the game that regularly checks which date your device is set to. If the date is set in the future and the game is then opened, you will theoretically receive offline income for this period, but the game will then remember this date, and you will no longer get offline income until you reach this date again.
Note that if you change your device time forth and back, without opening the game, nothing will break and everything will be working as usual.
Unfortunately, we cannot help you with this, as this cannot be avoided except by reinstalling the game or by reaching the date again. To see how far you've set your device time to the future, please contact us with your User-ID.
Please refrain from changing your device date & time when playing any of our games to avoid running into this issue.