Hi there @Tony1up, sorry to hear about the issue you're facing.
As you noticed, in File Explorer, a gray “X” icon can appear on a file or folder in your Dropbox folder.
This is a Windows icon and not a Dropbox icon. It indicates that your file or folder may not be syncing with Dropbox. To fix this, try the steps in this article about fixing syncing issues in Dropbox. If that doesn’t fix it, you can contact Microsoft support.
I hope this helps!