Sorry, I misunderstand the question. The registry above actually stores the Twain configruation only, so that's not the problem you have.

The scan source info is stored in the user's attributes in the repository whom is used to access the repository when open Laserfiche scanning.

For example, user A (Windows user) opens LF Client and login to a repository B using  Laserfiche account C, then scanning would query the user C's attributes and try to find acctribute key like [Scanning-A]ScanEngine-UserMachine(or [BasicScanning-A]ScanEngine-UserMachine) and read its value. If the attribute cannot be found, then the dialog will popup to ask user to choose a scan source.

So please check the user(which is used to login the repository in client) attributes to see if there is already key like that and what is the current value inside. Also try clear the attribute and see if that can resolve the issue.