For best performance, always use the Dropbox app on your computer when renaming, moving, copying, deleting, sharing, or unsharing folders, especially when they contain a very large number of files. We don’t recommend using dropbox.com or the Dropbox mobile apps when dealing with a very large number of files.
Set up and change Dropbox permission settings
Permission changes in Dropbox require all team folders and shared folders (namespaces) within the folder structure to be checked. This ensures the permission changes do not break any existing permissions set by admins. The more namespaces that exist within a structure, the more time it can take for a permission change to take place.
For example, you may want to share a folder that is nested in another folder within a team folder. To do so, permission settings for all of the namespaces for the folder structure will need to be validated before the permission change can be applied. Learn about Dropbox shared folders.