A locally quasi-convex abelian group without Mackey topology

We give the first example of a locally quasi-convex (even countable reflexive and $k_{\omega }$) abelian group $G$ which does not admit the strongest compatible locally quasi-convex group topology. Our group $G$ is the Graev free abelian group $A_G(\mathbf{s})$ over a convergent sequence $\mathbf{s}$.