Problem when moving an exported DNG from one folder to another

Not sure if this is a bug or user error but here's my problem.

I have several raw images that I import into LRC from my camera, do my edits, and convert to DNGs. I then export the raw images AND the DNGs into an "inbox" folder on my harddrive, and then drag the files from that folder into their separate product folders (which is easier than selecting each folder in the LR export box). Then I drag the DNGs into photoshop, which opens Camera Raw for import. This has worked fine for weeks with hundreds of photos. Last week, I did the exact same process, except when I went to import the DNGs into photoshop, I received an error that says "Could not place [file name] because no parser or file format can open the file." But when I drag the files back into the inbox folder and try to import them from there, it works as expected. I've tried creating new folders, different naming conventions, etc. but it seems like out of nowhere, once the file has been exported into a folder, it can't be moved out of that folder or it gets somehow corrupted for use with photoshop.

Its a really weird specific problem that I'm hoping someone has some advice on!