Sony Xperia Z ultra STUCK ON SET UP

I got the phone today. Set it up for my girlfriend who is going to use the device. Everything is working as it should except that every time she hits the power button or the phone sleeps automatically , a Sony Xperia logo appears and RESETS THE HOME SCREEN AND THE SETTINGS. I have no idea why its doing this and since its the first time in a long time that I had any kind of issue with a phones software, I don't know what to do.

I will be comfortable doing any kind of custom rom update if it's necessary and if there is a complete guide on how to do it. But I rather keep it stock for her.

Thank you for the answers!