Hey! Thanks for the piece of advice escapefrom3dom. Unfortunately I have tried rescanning the blockchain multiple times during the last years and, although it has worked a few times, I still have the same problem as uninstalling and installing again:

Rescanning is less time consuming but doesn't usually work, and I have verified myself that, when it doesn't work, it won't work until next reinstallation. Reinstalling, on the contrary, is more time consuming but works 100% of the times. Anyway, after a few stakes, the balance keeps getting wrong in both methods, so the problem remains.

As I said before, it is not a big problem, funds are safe and only the displayed balance is wrong.