How I fixed it by mistake. I found out I could run xcode 9.2 on a new drive and compile and run the same code fine. It looked like there was some issue with certificates, I deleted all my certificates on developer.apple.com and a made a new one ( a Mac Development Certificate ) but this didnt work when I tried to use it, same problem. In Xcode, I went into preferences->accounts->Manage Certificates and created a Developer ID Application certificate. I went into the apps target->general code signing and changed the Signing Certificate to this one. It now compiles and runs fine. I know this isnt a proper solution and will do a clean install in a new drive soon, but at least I can carry on coding and it might help someone else figure out the exact problem.

Hi, did you get any further with this, I need to do something similar ?