The multiplicity-free holonomy conjecture for finite groups

Let $H$ be a finite group. A Bieberbach group is a torsion-free crystallographic group, and its holonomy representation is the representation of $H$ on the translation lattice. The representation is $\mathbb{Q}$-multiplicity free when no irreducible $\mathbb{Q}$-representation occurs with multiplicity greater than one.

Multiplicity-free holonomy conjecture. For every finite group $H$, there exists a Bieberbach group $\Gamma$ with $\mathbb{Q}$-multiplicity-free holonomy representation $\phi_{\Gamma}$.

This conjecture concerns which finite groups can occur with especially restricted holonomy representations; the supplied text attributes it to the cited source but gives no resolution.