I believe I've identified the problem. It's not related to SmartPSS, my Windows firewall, or antivirus software; instead, it appears to be an issue with my internet service provider. Today, I attempted to install SmartPSS on another laptop and connect to my home Wi-Fi network, but I still couldn't get the devices online.
However, when I connected the laptop to my mobile hotspot, which uses a different internet service provider, I noticed that my remote XVR devices started showing as online. I've reached out to my ISP and requested them to investigate whether the IP addresses (47.74.188.221 and 47.74.157.160) of the Dahua server are being blocked. If they are indeed blocked due to excessive data traffic from these IPs, I've asked them to unblock them. Although I haven't received a response with a report yet, I believe this is the root cause of the issue.
I will provide updates once I confirm whether unblocking the IP addresses resolves my problem.
I want to express my gratitude to everyone for the valuable suggestions you've offered.