it's "working" now, so I suspect the problem is related to the hashing function. All files in the root of the 1st shared folder are immediately listed (and, presumably, shareable). Files in any sub-folders, however, are not listed/shareable until the hashing of the first folder is complete and are then listed one at a time (as they're hashed?).

At the very least, they should be immediately listed in the Library view, even if they're not actually shareable. This is what appears to be happening in the root of the shared folder, so why not extend that same functionality to the sub-folders?