My security camera send files to ftp server, which is a Synology NAS. All working well, except, the thumbnails will only load when I scroll to them. They start off being the generic icon for a movie file, and when they are within the field of view they load to show the thumbnail.

This is really slow to scroll through and look at thumbnails, as you have to wait several seconds for them to load.

Is there a way to force the entire folder to load all thumbnails?