As seen in the screenshots, I've had 3 images seemingly stuck in "syncing" status for months, but have no idea where/what they are because no errors come up. When I look from the LR desktop side, all is in good order so I assume it's something specific to LR CC.
No these techniques did not work. As shown in my original screenshot, I am not able to locate any files that are actually syncing. When I try the flag/rating trick, I am always left with 3 mystery files "syncing".