Well - almost all posters here are hit by the same issue, and fail to read Ivan's the original post, explaining about the need to working port forwards.
The other potential issue very few people complain: Private trackers seem to kick and ban the NAS Download Station (DSv3, introduced with v3.8.x) for still _unknown_ reasons. Appears the private tacker operators are not willing to tell their customers / trustees _why_. So impossible for QNAP to change anything.
[udate] Yes, limiting the upload (sharing, to the Internet) bandwidth on Download Station does implicitly limit the max download rate (Internet to the NAS) by a factor of 10. Thank you (non-QNAP-)Jason for the additional common cause. AFAIK this limitation is gone in DSv3 (available since v3.
That's all there is ... no rocket science. closing this endless "my DS does not work or is slow* thread now.