I haven't tested the Opauth instagram driver, but I checked the code, and it works similar to the facebook driver, which I have tested and which works fine.
It's the internal driver that intercepts the callback URL, and sets up the OAuth session, using the code passed in the URL.
It looks to me that in your case, the callback doesn't arrive at the Opauth callback processor, but directly at a method in your code.
Due to a restructure of our apps I currently have no test environment. There is no need to use routes, so with these routes it will definately not work.