Hey there mariorenzi, welcome to the forums!
I would suggest restarting the device, by removing the battery then reinserting it and turning it on.
If this doesn't change anything you might want to try Factory Resetting your device to see if this solves the issue, even though it sounds app related, and it sounds like you have already tried reinstalling Gmail, because if you haven't please do so.
If none of these help please get back to me!