A non-existence result due to small perturbations in an eigenvalue problem

We consider a well-posed eigenvalue problem on $(a,0)$, depending on a continuous function $m$. The boundary conditions in the points $a,0$ are depending on the eigenvalues. We divide $(a,0)$ into small intervals and approximate the function $m$ by a simple (step) function $m_S$, constant on each small interval. The eigenfunctions corresponding to $m_S$ do not exist.