Hard to say. What system have you got fitted? RT6 or SMEG?
However before you panic, it is a very common issue that Bluetooth can be the cause of reboots. The problem is compatibility between a paired bluetooth phone and the Head Unit. Smart phone system software updates are released generally a lot more frequently and this can cause problems with vehicle head units concerning the bluetooth profiles.
See my post in the telematics section here for what to do regarding this and to identify if it is the issue:
viewtopic.php?p=661203#p661203
If you haven't paired a phone yet or the fix above does not do anything, check the firmware is up to date (which may have a bluetooth compatibility update included in it for later smart phones).
If that fails and if you have some warranty when you bought the car I suggest you use it. Citroen / DS won't fix these - they can send them off to the Clarion Centre for repair which is quite expensive. Reboots can happen because of poor cooling in the dash where the units are - there's very little air circulation in there, or it can be the flash storage has become corrupt / work in the Head Unit.