When I import a zip archive with images into the assets, a folder with the name "__macosx" is created in addition to the images. This has the same content as the archive, but the file types are not supported.
Most likely the files in the folder "__macosx" are the resource fork of the JPGs. This is created automatically when the file is saved on the Mac. This can be prevented by saving the image from Photoshop using the command "export for web". Please try this solution.