Sonarr suddenly can't talk to qBittorrent

Sonarr version (exact version):
Mono version (if Sonarr is not running on Windows):
OS: Windows 10
Debug logs:2022-11-15 06:53:27.6|Warn|ProcessDownloadDecisions|Couldn’t add report to download queue. NCIS S20E07 720p HEVC x265-MeGusta

[v3.0.9.1549] NzbDrone.Core.Download.Clients.DownloadClientException: Failed to connect to qBittorrent, check your settings. —> System.Net.WebException: Unable to connect to the remote server —> System.Net.Sockets.SocketException: No connection could be made because the target machine actively refused it
at System.Net.Sockets.Socket.DoConnect(EndPoint endPointSnapshot, SocketAddress socketAddress)
at System.Net.ServicePoint.ConnectSocketInternal(Boolean connectFailure, Socket s4, Socket s6, Socket& socket, IPAddress& address, ConnectSocketState state, IAsyncResult asyncResult, Exception& exception)
Description of issue: Sonarr suddenly can’t connect to qBittorrent. Nothing was changed, there was successful contact overnight, several files were passed over and successfully downloaded.
This morning - no connection, LOG shows the connection was actively refused. All settings look normal, and as I said, nothing was changed.

That error generally means nothing is listening on that port a firewall is blocking the connection. Since it’s using then the firewall shouldn’t be blocking it, though confirm that the network type is correct on your system (Private vs Public) and that qbit is correctly listening on port 8080 (should be able to open that URL in your browser).

Well, this is weird.

The problem has simply ‘gone away’. Sonarr and qBittorrent are now communicating OK and several downloads were requested and completed overnight.

Yesterday afternoon I did try to access qBittorrent via the browser and had no problem. This was at the same time that Sonarr would not connect.

So I guess this can be closed as an ‘unknown’.