Interestingly... I had a FXpansion download totally crap out on me a few days ago, and I was using FDM at the time. A couple of files came through ok, with barely acceptable bandwidth, but I did have the total failure (after 96% of 3.5GB downloaded) and a massive number of low-bandwidth attempts because the server wouldn't allow FDM to create new sections (and no, I did not accept "37 hours @ 100KB/sec" or some such nonsense, so killed those failed attempts early on). Switched over to using DownThemAll via Firefox on both Mac and PC and things seemed much more stable and consistent... bandwidth from overseas wasn't stellar, but I was able to get in the 500KB/sec range per file...
Maybe FDM itself has issues and/or certain ISPs are putting up roadblocks? Not sure... Just think it's interesting that you also had a totally failed download with FDM... which, obviously, is not supposed to happen at all, because the servers supposedly support "range requests", which is how those managers divvy up the downloads... An unrecoverable failed FDM download would appear to be catastrophic, in relative terms...