I have two large files I've been downloading for over a week via ed2k. Both have lots of sources (one has nearly 50, both over 15). Until a few days ago, they were downloading intermittently and not very fast, but both of them were remotely queued on one or more sources nearly all of the time when not outright downloading.
Then, sometime around Tuesday it's like a switch was thrown somewhere. Neither of them will queue with any of their sources. I've been making occasional smaller downloads, some ed2k and some G2, in the meantime without noticing anything unusual; it's just these two big files that are acting like every single one of their sources dropped dead simultaneously a few days ago.
So, I don't think this can be a network issue. It's somehow specific to either these particular files, or to larger files in general. The smaller is 700MB and the larger nearly 3GB, while the largest size of any file I've had download progress on in the last few days has been under 5MB, so the threshold may lie somewhere between 5 and 700MB.