Images moved from Macbook to Dropbox folders not showing thumbnails and not opening

[FFI]

I have a dropbox family account of which I am the owner. All the images I have moved from my macbook pro to dropbox folders show the thumbnails and open on double clicking when I first add them. However, when I go back to the folders a short time later, the thumbnail image no longer shows and I have to right click to choose preview to open them (even though it is set as default to open). The images have a cloud images next to them and show zero bytes.  If I edit them from dropbox the thumbnail appears again and opens ok. It is a pain having to open every image to see what the thumbnail is and is making my workflow much longer. I have gone into 'get info' and set preview to open all files of this type but it doesnt seem to make any difference. Dropbox is still at the top of the 'ope with' list when I right click the image to open it. Help please. I am in my sixties and not particularly technology savvy although manage just fine unless its technical. 

[Hannah]

Hi there, @FFI, and thanks for reaching out to us.

If you select your images, right/control click on them and choose to make them available offline, does this issue go away?

Let me know.