A tracker is down, all torrents using this tracker will eventually time out and go into error state. As soon as deluge sends announcement for a torrent in error state it stops considering this torrent as error until it times out again, this leads to large scale fluctuations of the error state 'folder' - initially it is filled with timed out torrents, in 10 minutes deluge sends next announcement and error folder becomes empty only to be filled again after torrents time out in a minute. I believe torrents which previously timed out should be considered to be in error state until successful announcement, not just after any announcement.
rc5, hardy 64