Where did you buy it, any support from the seller? What kind of cameras and how many do you have. How often is this happening? has the system been running for some time or is this like this out of the box. First thing you might want to do is backup your configuration to a thumb drive so you do not have to re set all your settings every time this happens. Do you have active log file running so you can see what and whom is accessing your system. Is this a business or home system? Any chance of somebody remoting in and rebooting it for fun just to make life happy for you. Hopefully you have it locked down with all user names and passwords secure. If this system is open to the internet you might better make sure its locked down. I guess I just gave you a few things to look at.
As far as a solution, a little more info would be good. Their is firmware updates out there but unsure about this model according to the Dahua
wiki page.
I believe the latest build 3.210 released in 6-17-15 according to Nellys security website.
Dahua DH-NVR4832-16P-4K 32 Channel 4k POE NVR for IP Cameras - Nelly's Security
I have had quirky issues with these 4k NVR's but not rebooting and lost settings.
