$-\Delta u=1$ in $D$

$\frac{\partial u}{\partial\nu}+(x_1^2+1)u=0$ on $\partial D$

where $D=\{(x_1,x_2) : x_1^2+x_2^2<1\}$.

What is the reason for the warning?

restart;
f := (x, y, z) -> 1 - x^4 + ln(x^4) + z^4 - y^4 - y^4*(ln(z^4) - ln(y^4));

with(Optimization);
Minimize(f(x, y, z), {x^2 + y^2 - z^2 - 1 = 0, 0 <= x - 1, 0 <= y - x, 0 <= z - y});
Warning, no iterations performed as initial point satisfies first-order conditions
                 [0., [x = 1., y = 1., z = 1.]]