I guess you have forgot to set the right IP address, subnet mask and default gateway. You should regard your switch as a device like a computer and make it connected to the Internet.

The length of the Ethernet cable won't be a cause of the problem but the quality, maybe you can try another Cat.5 or above cable. Is the old mode IP camera a standard PD? Or have you applied some PoE...

I will feedback it to their support to urge them to solve the problem soon. But I think it may be because there are little people need to disable this function.

Expect the IP of the rputer's LAN IP, can you Ping the devices's IP in the LAN? You can Ping the router's LAN IP 192.168.0.1 for example even the VPN does not exists.

Hi,what's the model No. of the product? You can try to disable the wireless password and check if you can connect.

Yes,you can add similar PLC product in your network. You can pair the new one in the same room with your existing PLC. Then put it where you want.