I have some problems with your new versions of nuget packages (v12.2.1100).
You can easily reproduce it with the following few steps:
-Create in Visual Studio 2017 (or 2015) a new WinForms project (C# or VB anyway)
-Add latest Oracle NuGets (Install-Package Oracle.ManagedDataAccess -Version 12.2.1100)
-Build the solution
-Add some settings to the project
-Save the settings file
Now you get the error. It cant read/write the app.config file:

BUT if you downgrade to the previous release (Update-Package Oracle.ManagedDataAccess -Version 12.1.24160719) and rebuild, it works well.