Hu-Yau's conjecture on symplectic resolutions and Mukai flops

Let $W$ be a symplectic variety, and let $Z\to W$ and $Z^+\to W$ be projective symplectic resolutions. A Mukai flop in codimension $2$ is a birational transformation that becomes a Mukai flop after removing subvarieties of codimension greater than $2$. Hu-Yau's conjecture. Any two projective symplectic resolutions of a symplectic variety are connected by Mukai flops in codimension $2$. This is known for four-dimensional symplectic varieties and for symplectic resolutions of nilpotent orbit closures, and the paper proves it for quotients ${\mathbb C}^{2n}/G$ by finite subgroups $G<\operatorname{Sp}(2n)$; the general statement remains open.