I use a Windows 10. X will mark an image for deletion, Z will reverse that. So I don't know what is happening on your computer. What exact version of Lightroom CC are you using? I'm using version 2.2. Also, take note that I'm referring to the images in the cloud. I'm not looking at images on my hard drive.
With Lr CC all photos are managed in the cloud. Importing uploads them to the cloud. Lr CC does not retain a connection to the original images on the hard drive like Lr Classic does. After the photos finish syncing you can remove them from your hard drive. I recommend making a backup of them before you do this though. When you delete a photo from Lr CC it removes it from the cloud. If you have turned on the preference to store locally, the local copy will also get deleted.