We are not completely aware of why systems are showing offline periodically. From what we can see at this point, the issue seems to correlate with the DHCP lease time in the router that the device is connected to. We are working to confirm the cause of the issue, and to find a more effective resolution.
Customers have reported success with increasing the DHCP lease time in their router, and decreasing the frequency of offline instances.
The issue does not seem to have anything to do with the version of Zsight that you are using, as the issue is the same across Zsight, MeShare, PC ZViewer, and our internal tools. If you want to test with older versions of Zsight, they are available here. http://files.zmodo.com/Software%20Files/Phone%20Apps/