After you add user to Remote Desktop Users Group but can’t remote
I have solution for this case by you can add directly to RDP-Tcp permission
How To Add a user or group from permission lists
1. Open Terminal Services Configuration.
2. In the console tree, click Connections.
4. On the Permissions tab, in Group or user names:, select the user or group you want to add, and then click Add.
To perform this procedure, you must be a member of the Administrators group on the local computer, or you must have been delegated the appropriate authority. If the computer is joined to a domain, members of the Domain Admins group might be able to perform this procedure. As a security best practice, consider using Run as to perform this procedure.
To open Terminal Services Configuration, click Start, click Control Panel, double-click Administrative Tools, and then double-click Terminal Services Configuration.
You must use the Remote Desktop Users group to control remote access to Terminal Server and Remote Desktop for Administration.