Hey Rafacandido,
Thanks for the question. Let’s see if we can isolate the issue further. To do so, try restarting/resetting your device:
Turn your iOS device off and on (restart) and reset
http://support.apple.com/kb/HT1430
If the issue persists after a restart, let's try a reset of your settings as outlined below:
Reset iPhone settings - iPhone
http://help.apple.com/iphone/7/#/iph7a2a9399b
Reset iPhone settings. Go to Settings > General > Reset, then choose an option:
Reset All Settings: All your preferences and settings are reset.
And finally, if the issue persists you can try a back up and restore as new:
iOS: How to back up your data and set up your device as a new device
http://support.apple.com/kb/HT4137
After erasing and setting up as a new device, your device is now in a factory configuration. Test to determine if erasing and setting up as a new device resolved the issue. Content on the device may have caused unexpected behavior.
If the issue is still present, you may want to contact Apple Support.
Thanks,
Matt M.