Have you created a basic addin from scratch to see if it's something to do with your addin?
Make sure you've cleaned and rebuilt your solution, and check out the build location to see if any dll/pdbs other than Kope
I've found issues with this, and I'm not sure what's causing them (the Add-in Manager?), but what worked for me was when I attached the debugger to the Revit.exe process, I changed the settings as shown in the image.
If that doesn't work for you, you're going to have to provide a lot more information about what your processes and (VS) settings are. Are you using the addin manager? What are all of your VS debug settings? Can you provide an example solution?