The N9 of my girlfriend has the problem of mixed sms. It started the 31 december a few minutes before midnight, she lost all her sms and then since this moment only a lot of sms problems. She send sms to a friend and the sms is shown in another discussion.

She's telling me that her iphone was better

The only particular app installed is N9QTweak. Is this the problem?
I dont want to flash the mobile. I already reset it but still have those problems.... what can I do?