This happens more often with network drives than physically attached ones, and I, for one, had this issues happening with Synology NAS. A file or a folder that is most likely not damaged and most likely was accessible previously, is now inaccessible on macOS Finder. The real odd ball is that other devices and apps have no problem accessing it.
Tagged Finder
Fix macOS Shared Folder ‘Not Found’ Error
While Mac handles vast majority of things nicely without too much asking questions, keeping network connection to a NAS drive is not one of them. If you happen to be on WiFi, and your Mac is likely to go to sleep frequently (i.e. it’s a laptop), you will see an annoying error message anytime you try to reconnect to NAS, “cannot be opened because the original item cannot be found”.
Force Empty Trash Can on macOS
If you have just transferred over to Mac, the first problem likely to notice is deleting files. With the migration-related apps running in the background, file permissions can get wacky easily. Any times file systems or file permissions are being modified, you can encounter this issue again. While this problem is less frequent since California-based Mac names, let us assume for a moment you have a reason not want to reboot your computer and have encountered such an issue.
Force Spotlight Indexing on macOS
With the release of High Sierra, I assume most Mac users had a chance to upgrade any number of drives to APFS from HFS+. Now you may have noticed it by now, but apparently High Sierra has shipped with some glitches in APFS related tools. My mdutil search has turned up “Index Enabled” for all of my drives, but the actual index had stopped updating since Public Beta.