Three of five Qvis IP Cameras suddenly gone Offline

[Fozzie Bear 0]

I have a number of Qvis EYEVIP-5-FW turret POE cameras and three Qvis Viper 5mp POE bullet cameras connected to a Falcon NVR. They have been working perfectly for about 8 years. However a few days ago when looking at the cameras through the SuperLive Plus App on my phone, I noticed three cameras were offline.

On return to home sure enough two EYEVIP-5 and one Viper Bullet were not showing on the NVR. All the cameras are connected to a POE hub and configured with a local static IP address of my LAN so I can connect to them individually. They are not plugged in to the POE sockets of the NVR.

I have rebooted each camera by unplugging and reinserting the POE connection via the cat 5 cable however none of them have come up again. At first I thought the POE switch might be failing as the green leds on the switch for the three affective cameras were dimmer than the working ones. I have therefore purchased a stand alone POE injector and connected each camera in turn to the new injector. Again none of the cameras come back online.

I can ping each defective camera but cannot access the cameras web interface, although can still access the working cameras.

I thought there must be something common with all the cameras that has caused this e.g. POE and it seems strange that three cameras have all died at the same time.

As an aside I have fairly recently changed my broadband provider and installed a new router. I had to change the default 192.168.1.x subnet on the router to my previous 10.0.0.x subnet and changed the DHCP scope from .2 to.199 as all the cameras had .200, .201 etc etc static addresses above the DHCP range. I haven't however configured static DHCP allocations in the router as they all were working perfectly and I can ping their static addresses?

I have not taken any of the cameras down yet to physically inspect them as I don't have time just now. Does anyone have any suggestions as to what I can try next or what the issue might be, other than they have died?