Happens randomly but only once a week on average.

Bit annoying but not the end of the world, as I wasn't expecting a reversing camera on the car when I bought it last year anyway.

Rather nice though for getting that little bit closer than the sensors do

 

Dealer for a warranty check is it then I suppose?

Anyone else had this randomness of a failure?

Yes, though less frequently than each week. Sometimes fixed by shifting out of, and back into reverse. As it's an intermittent issue could be difficult for the dealer to diagnose...

Happend 4-5 times since the car was new (1,5 Years) 

as mentioned fixed by shifting out of, and back into reverse.

I get the same thing, very occasionally. I also once managed to (somehow) have the rear cam showing while I was in D driving forwards too which was cool. It deactivated at 20km/h though :(