Telerik openaccess does not read SQL-server tables, can it be caused by the double backslash in the connectionstring?

I'm working on a C# application, based on Telerik's OpenAccess technology.

The following piece of source code does not give any results (although the corresponding table contains a lot of data):

List<Setting> lijst = new List<Setting>();
try { 
    lijst = database.GetData<Setting>().ToList();
}
catch (Exception e)
{
    log.Error($"Exception: [{e}], Message=[{e.Message}]");
}
log.Debug($"Count=[{lijst.Count()}]");

However, the following piece of source code (from another, similar program) does give results:

internal static IEnumerable<Lift> GetAll(IDatabaseConnection database)
{  
    return database.GetData<Lift>();
}

The only difference is can find, are the connectionstrings (according to the watch-windows):

• Non-working application : "Data Source=localhost\\SQLEXPRESS;..."
• Working application : "Data Source=localhost\SQLEXPRESS;..."

As you can see, one contains a single backslash, the other a double one.

However, both strings are created the same way:

• Non-working application : Settings.DatabaseAddress = @"localhost\SQLEXPRESS";
• Working application : Settings.DatabaseAddress = @"localhost\SQLEXPRESS";

Am I on the right track and are those single/double characters indeed an indication, explaining the wrong database behaviour, or am I on the wrong track here?

For your information: I'm working with Visual Studio 2022, version 17.5.5.