DVR Dropping and changing ip address

[Jmc56 0]

I am working with a DVR that is older than Moses. The unit worked 3 weeks ago when it no longer connected to the network. I checked the ip address and it had changed. We had planned an upgrade to the local network so we added a static ip address 71.118.48.180 with the proper subnets and turned off DHCP. This worked for about 24 hours. The next day the ip had changed to 192.168.1.1 (subnet and gateway also changed, each time it changes it is different) and the cameras were no longer accessible. The DVR is not locking up as the front panel switches allow you get right in and change the ip back and all works for about 24 hours. This happens almost 24 hours later almost to the minute. The owner accesses the cameras through a free program called Netguard on an Iphone I also set my Android to use the same software. The application really only allows you to see the camera feed not do anything else. The cameras still show on the in-house monitor and are recording properly. The unit is connected through Ethernet to a gigabit switch direct to the ISP modem. The network is working fine as we have about 300 devices on this net.