I am having a similar experience in Visual Studio 2017. I have uninstalled and reinstalled the SDK extensions which had no effect, and then did a visual studio repair which also had no effect. The one thing I noticed (which may not be related) is that when adding an SDK item such as a button, the icons that are added to the project have their "Build Action" property set to "Resource" instead of "AddInContent". Other than that, there doesn't appear to be any problems with the created classes.
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