As others have noted (see e.g. here), the change from using a cython command to the "cythonize" function call within skimage/_build.py has broken the build process on some machines. Cython files don't get compiled to .c files automatically and the build fails with errors such as:

Calling Cython manually for all the files works, but obviously this is not a solution. Does anyone know what's going on here?

Juan.