I've been running KTorrent 24/7 for years on Kubuntu, currently on 18.04.4. About a week ago I noticed none of my seeds were uploading, and if I tried to download a new torrent, it would show up in KTorrent, but never download. I assumed it was a network issue with my ISP, but I fired up a torrent client on another PC on my network, and it worked fine. KTorrent wasn't showing any errors, it was just stalled.

I installed Transmission, configured it to use the same port as KTorrent, and used it to open all of the torrent files in ~/.local/share/ktorrent. They all worked fine, and new downloads worked fine.

I've confirmed that I can connect to KTorrent's network port from elsewhere on the Internet.

The only entries in the log that look like errors are:

Error happened during parsing : Missing nodes or nodes6 parameter

Authentication to <IP address> : failure

On some of these <IP address> is my address.

strange, what did you change before that happened?