When you copy files in the Finder, particularly between disks so that APFS doesn’t merely clone the original in the twinkling of an eye, a small circular progress icon is shown next to the file while copying takes place. In Mojave 10.14.3, those progress icons can become frozen, leaving the icon in place even though the copy is complete.
This bug doesn’t appear consistently: the great majority of the time, Finder behaves as expected. The icon appears when copying starts, the circle fills rapidly, and is then removed. Just recently I copied a batch of images, some of which were several megabytes in size, from my internal SSD to an external SSD. For several of those files, the copy progress icon appeared but made no further progress, although the files were copied fully and correctly. This left the icons in situ whenever I browsed the contents of those folders.
In Finder column and list views, it appeared that those files were still being copied, even though the Get Info dialog showed that copying was complete, and the files could be opened normally.
In Finder icon views, those files were marked with a X, implying that copying could still be cancelled, although the X proved non-functional.
Even leaving these items for more than 12 hours failed to correct this. I was unable to perform First Aid on that external volume because Disk Utility couldn’t unmount it, as Finder was still using it. I therefore forced Finder to restart, which freed that volume up so it could be unmounted, and First Aid then reported that the volume was healthy. After that, those residual icons had vanished and the files remained intact.
If you start seeing stuck progress icons in Finder views, the answer appears to be to force the Finder to restart. Hopefully you won’t be as surprised to come across them as I was.