Folder won't resync after moving them out and in

So I got a problem and I don’t know if it’s a bug. If I move a folder containing images into my Nextcloud folder on macOS the client synces and all the files will be uploaded to the cloud. But as soon as I move those files to my Desktop again and delete the files from the webUI in the trash bin they won’t get uploaded again when I move the folder in the Nextcloud folder again. I hope you get what I mean. It only synches the folders but not the images or videos. What’s the issue?