To answer directly to your questions: - M4 is always plugged and connected to the LAN (and to the ISP router). And, camera's issue apart, it works fine. - I tried to physically connect together only...

@TP-Link Thank you for your reply. M4 is always physically connected to an ISP router, using a 1Gb Ethernet cable. The NVR is connected to the same LAN, 1Gb Eth cable too. - If I connect the camera...

I have some devices (IP cams) that use protocol ONVIF on port 8999 to connect to a NVR. They use a proprietary protocol on port 80 to connect to their own app too. Now... when they are connected...