I started playing with Fopnu and accepted default settings just to get a feel. I'm now a fan, and transferring so much that I need to get storage off my system drive.

I changed the download folder in settings and moved the contents of the original folder to the new location and started up Fopnu. Fopnu lists all my in-progress transfers as missing and wrote new 0_incomplete files to the original default folder. Forcing a recheck does not seem to help.

Starting over is a possibility, but I hate to lose the progress I'd made on the incompletes. Is there a step I should take?

It’s a classic "mid-stream" migration headache. The reason this is happening is that Fopnu (and many similar P2P clients) stores the absolute file path for each active transfer in its internal configuration database at the moment you start the download.

Changing the "Global" download folder in Settings usually only affects new transfers added after the change. It doesn't retroactively update the metadata for files that are already "in flight."

I don't think you can change the destination folder while in fopnu.

There is something you could try if you search and find those files again.
First stop those transfers.

The "Re-Download" Trick (Step-by-Step)

Since Fopnu tracks files by hash, not just by name, your method works by tricking the client into "discovering" the data in its new home. Here is how to execute that safely:

   Clear the Ghost Files: Delete those 0_incomplete files that Fopnu automatically created in your old folder.

   Move the Real Data: Manually move your original .0_incomplete files (the ones with progress) into your new storage folder.

   Remove from fopnu : In the Transfer list, right-click the "missing" entries and Remove them. (Don't worry, this only removes the database entry, not your moved files).

   The "Discovery" Phase: * Search for the files again

       When the "Save As" or "Download" prompt appears, point it directly to the new folder where you just placed the incomplete files.

   Hash Check: Fopnu will look at that folder, see a file with the correct name and hash, and should automatically start "Checking" the bits. Once it hits 100% of what you've already downloaded, it will resume from that point.