Malle–Robinson conjecture on the number of irreducible Brauer characters

Let $H$ be a finite group, let $B$ be an $ell$-block of $H$, and let $D$ be a defect group of $B$. The sectional $ell$-rank $s(D)$ is the maximum of the ranks of elementary abelian $ell$-sections of $D$. Malle–Robinson conjecture. One has

$$l(B) \leq \ell^{s(D)}.$$

This conjecture bounds the number $l(B)$ of irreducible Brauer characters in a block by a quantity determined by the sectional $ell$-rank of its defect group. Its resolution status is not specified in the source.