Just recently, my Kemper sounds different. I recently did a gig where I borrowed a friend's Kemper for another guitarist in the band to use. I did a backup on mine and a restore on his to duplicate the two Kempers so all of our tones would match perfectly. Any changes made on one would be backed up and restored on the other.
All went well through the gig. When I got my Kemper back home, playing it through the same cabinet with the same guitar, all of the profiles sounded a little bit thinner with a bit more edge. Enough so as to make the amp not a pleasure to play through anymore. I've rebooted. I've done a system update from 5.3 to 5.1.0. I've done a restore back to a date before I started copying back and forth with the other Kemper. I've gotten the other Kemper back and A/B'd it with mine and there is definitely a difference. The other one sounds beefy like mine used to. I've even done another backup on the other one and restore to mine.
I've gone through all the pages in the Output section and compared them both. All settings are identical. I've done the same in the System section and all setting are identical.