FVC-70 registers with Mgmt Software V7.31.003 and loses connection after 15 minutes

Problems started about 2 weeks ago with all phones not working and FVC-70 not maintaining registration thru the Management software.  All red lights on Talkswitch TS-350 IP phones.  Resets did not change result.  Tried a second FVC-70 - same problem.  Changed from Static to DHCP with table entries - no change.  

After a reset or reboot, the FVC-70 would detect, connect and make calls.  Within an hour, the Management software would lose connection and report "No systems detected.  Detection failed: 192.168.1.4 (IP conflict or misconfigured subnet).  I would then remove DHCP entries, reset and reboot and the same FVC-70 would register at 192.168.1.17.  One hour or less later, same lost connection. 

I then purchased a used working FVC-70 and got the same results.  I have now replaced the main router and disconnected all devices except the Windows 10 computer that has been supporting the original FVC-70 for over 5 years.  No change in performance.  According to the Router connected devices, the FVC-70 is connected, but the FVC-70 reports no systems found or detects a system and then says it cannot connect to the system 192.168.4:9393 and suggests that this is a remote location connection.

Has anyone seen this type of problem?    Thanks in advance for any and all advice!!!