Both of those stories downloaded fine for me with skin set to 'EnchantedFogWide'.
Have you tried the usual generic remedies? Restarting calibre, rebooting your computer?
Because I don't think there's anything wrong with FFDL here. I suspect either the site isn't sending all the data, or it's getting lost along the way.
Do you get any errors viewing the site around the same time as FFDL gives you errors? Are you trying to do lots of updates all at once?