I’ve had this problem too. It’s shocking how this is allowed to happen, as it has major consequences. I have no idea how to replicate the issue, it just pops up occasionally, and every time I catch it, I wonder how often I didn’t.
Indeed, the problem may have popped up only to solve itself eventually, or I may have actually delivered old or in-progress assets to clients without even realizing it.
Thanks for the disk cache tip! Saved me some trouble.