Hello @Wiwi&masterblast - I am sorry to hear that you lost your piggy bank again.
The studio believes that the most important way to learn about
whether and how the players enjoy different features and events they make for
them is to do what they call AB tests. By giving some players a particular
event/feature, and others another event, or maybe no event at all, they can
compare the data from those different groups and learn how appealing and fun
different elements of the game are. This is how they make sure that they only
give their players what they really enjoy!
In this case it appears you have been randomly selected (it appears again - based upon your post) to have your piggy bank removed. These tests run for a finite period of time so hopefully your piggy bank will return soon. In the meantime, to ensure it is not a temporary glitch, please clear your cache, make sure you have the most recent update of the game and turn off your device for at least 10-15 seconds. When you turn it back on, if your bank hasn't reappeared, then it appears you are indeed in a test group. If so, hopefully your bank will return soon.