2010 Pathfinder Stereo keeps resetting

[Haitch2o]

Hi all, I have a 2010 Pathfinder Tekna. Every now and then, could be once could be 10 times, the stereo/satnav/touch screen unit resets. It turns off, the music stops, I get the Nissan logo and all starts again, this will happen at least once a week maybe 2 or 3 times a week. Nothing specially sets it off, its been tested by Nissan but as it didn't fault at the time so they found no problem. It also sometimes freezes whilst in sat nav or phone, but that could be a different issue.
Does anyone know what the problem and fix could be?

Cheers