Hello,
I've noticed one file in particular of mine, has gone from 48% complete, to 26% over about a week of inactivity, then dropped to 1%, again over about 1-2 weeks of inactivity.

Its a 3.8gig file, and sources are few and far between. Why is the file reducing in size over time?

Any help or info would be great, cheers

Maybe there's a corruption within that file: Downloads "Jump" backwards

Check the file with Bitzi, if other users have rated the file then you'll get some idea if it's ok or not
How to use Bitzi

Even though the sources are few & far between, try to download a different version of the file...see whether that's any better.