Ok - so I'm dumb

Migrated my workspace, compiled and ran my web app. Then I thought I'd play around with a couple of new things. Put in some code recompiled and ... nada. Ok clear the cache... nothing. Then it dawned on me that I had not re-registered the 18.0 web app under a different name so it was just running my original 17.1 web app ... DUH !!!