I have experience exactly the same problem. Reboot, Assemble Raid, Reboot, in an infite loop. The web admin doesn't respond etc. Well, my machine rebooted (see my other threads about this problem) in the middle of a write. The RAID is lost. :-(
I've had my N5200 for a month now, and I have had so much problem that I have lost all my faith in the product as well as TheCus that I'm going to return it to my reseller.