Normally I see
"The breakpoint will not currently be hit. No symbols have been loaded for this document."
whenever the Add-In has not been added to a toolbar in ArcMap. In the case of Add-In buttons and tools, there is a property that you set upon creating the Add-In project in Visual Studio using one of the ArcGIS Add-In template that is called OnDemand. If OnDemand is set to true, I notice that no breakpoints will be reached while debugging the Add-In (even if the Add-In button or tool is already added to ArcMap) until you click on the Add-In button or tool. This is because the Add-In does not load I believe until enduser clicks on it.