In lambda calculus, starting from $KII$ we can get by a single $\beta$-reduction to either
Now, according to Church-Rosser, these should be reducing into a common normal form. But the first reduces to $I$ and the second to $\lambda y.\lambda z.z$.
Am I doing wrong $\beta$-reductions or the theorem holds only on some condition? I do not see a common reduct here.