[DanCooper]

Is there a way to work around this with Ember?

The Kodi Interface simply replace the movieset images path that you've set in the Settings => Moviesets => Files and Sources => File Names => Path with the path you've set in the Kodi Interface Movieset path settings (and change the slash/backslash if needed). That means with an "Ember" movieset image path e.g. Y:\Movieset_Images and a KI movieset path smb://MyServer/Movieset_Images:
Y:\Movieset_Images\die hard collection-poster.jpg will be become smb://MyServer/Movieset_Images/die hard collection-poster.jpg.

In addition to the lack of specification of the protocol (in this case smb: //), the problem is usually the lack of access rights or login data for this path. The simplest is if you store the login data for the entire server (path) in Kodi and not for each share individually. So not:

Code:

smb://USERNAME: PASSWORD@Server/Movies
smb://USERNAME: PASSWORD@Server/TVShow
smb://USERNAME: PASSWORD@Server/otherVideo

but rather

Code:

smb://USERNAME: PASSWORD@Server

Most of the time, only one login is used for all shares on a server.

Depinding on how you added your sources in Kodi the login has been saved for each share individually and possibly the movieset path login is not permanently stored.
There is a "passwords.xml" in the Userdata folder on your Kodi client that contains all stored logins for your connections. Check this file if you've added a login for the whole server or change it if needed. I've you've fix that is also no longer needed to store the login in the image paths.