Period-collapse conjecture for deleted Shi arrangements of root systems

Let $k\in\mathbb{Z}_{>0}$, let $\Phi$ be a root system, let $\Phi^+$ be its set of positive roots, and let $\delta\in\Phi^+$. Write $\delta^c$ for the complement of $\delta$ in the relevant root data, and let $\chi_{\mathrm{Shi}_{\delta^c}^{[1-k,k]}}^{\mathrm{quasi}}(q)$ denote the characteristic quasi-polynomial associated with this deleted Shi arrangement. Period-collapse conjecture. Period collapse occurs in $\chi_{\mathrm{Shi}_{\delta^c}^{[1-k,k]}}^{\mathrm{quasi}}(q)$ in all cases except when (i) $\Phi=A_m$, or (ii) $\Phi=B_2$ and $\delta$ is a long root. The conjecture predicts, in the type-$B$ setting, that for $m\geq 3$ period collapse always occurs in the characteristic quasi-polynomial of $\mathcal{B}_m\setminus\{H,H'\}$ when $H$ and $H'$ are parallel hyperplanes in $\mathcal{B}_m$.