You might also find your answer in the LastPass Enterprise Manual.
I added a user to a group that was assigned to a Shared Folder, but the user cannot see the Shared Folder?
When a user is added to a user group that is already assigned to a Shared Folder, they will automatically be added to the folder. You will be notified if the group is assigned to any Shared Folders before we add the user to the group.
If the user cannot see the Shared Folder, please ensure they were fully added to the group, they have generated their Sharing Keys, and that the folder is populated.
This may also be the case if you have used Active Directory/LDAP sync to provision your users into a group that has been pre-assigned a shared folder. In this case, you will have to remove and then re-add the user(s) from the shared folder.