Uniformity in Higher class Free Lie algebras

Let $\mathfrak{f}_{c,2}$ denote a free class-$c$ Lie rings on $2$ generators. We investigate the zeta functions enumerating graded ideals in $\mathfrak{f}_{c,2}(\mathbb{F}_p)$ for $c\leq6$, prove that they are uniformly given by polynomials in $p$ for $c\leq5$ and not uniformly given by a polynomial in $p$ for $c=6$. We also show that the zeta functions enumerating one-step graded ideals $\mathfrak{f}_{c,2}(\mathbb{F}_p)$ is always given by a polynomial in $p$ for all $c$.