@krammor Oops, sorry, my fault, the recently integrated bugfix commit caused a follow-up issue (and the test-suite didn't automatically test Unity 2017.4, so this unfortunately slipped through). It has now been fixed, a new spine-unity 4.0 unitypackage is available again.
You should now get 32 harmless shader compile errors, these are due to old Unity versions reporting errors of shader code branches which will never be active in this combination. So you can ignore these shader errors.
