The qBittorrent 4.x version originally deployed on the NAS was updated to 5.0.x after a package update, and it was found that all tasks could not connect to the Tracker server, and the web backend displayed 0 DHT nodes, and no UPnP port forwarding records could be seen in the router backend.

After repeatedly trying and even reinstalling the 4.x version for comparison, it was found that the solution was to set the network interface to "Any" in the advanced settings tab of qBittorrent 5.x, which could restore normal functionality. The Synology package version of qBittorrent defaults to selecting ovs_eth2 here, and it was unexpected that this setting was the cause.