As Björn mentioned, the “Release” flag disables the engine service which holds the web server.
When you launched it, did you use “build and run”?
Regarding building with clang, I’d like to know what extensions failed to compile and why? Was it your extensions, or some third party extensions? Note that we are switching to Clang as the compiler soon, so it’s good if you start making sure each extension actually works for you.