So, in my recent transition from an ancient Windows OS to a Linux distribution I installed Transmission for torrenting. I had a decent experience as a user who isn't super nerdy about this stuff with the Windows version I was using.
Using it with Linux has been similarly easy but for one thing. When trying to seed torrents, after about 10ish minutes, the torrents in the list will turn red and with the word "Stalled". I can pause and restart the seeding and it clears the "Stalled" from the item on the list but it will come back after a short while.
This never happened when I was using the Windows version and I haven't been able to find an answer about what this is supposed to mean in this context online.
Anybody have any ideas what this means and what I should do to fix this if its a problem on my end?
Edit: NordVPN is blocking the ports. Weird thing is, earlier this year before switching this PC to Linux, my ancient Windows OS was running Transmission and leeching/seeding just fine through NordVPN. 
i would still go with
journalctlto look for clues; logs containing errors, failures, or timeouts are great places to start.woof... this output is going to be a bear to look through for my non-techie self.
puts on my reading glasses
search for the words "error", "failure" or "timeout"