Torrents with dead trackers prevent the download of other torrents.
I had some torrents pending in synapse. Many of them belonged to a tracker that is currently down, and a few of them belonged to various other trackers that were currently working fine. The torrents with the working trackers where not downloading. After I paused all of the torrents with the down tracker, the torrents with working trackers began downloading immediately.
Before I had done this, the working torrents had been sitting in pending for a few days, and had gone through several client restarts and even a vm restart with no change. Pausing the torrents with dead trackers immediately fixed the problem.
I'm possibly experiencing the same problem, synapse stopped downloading but I'm not sure what's the best way to diagnose what's the actual problem.
Interesting, I'll look into this and see if I can find what's going on.