Holomorphic differential locus conjecture

Let $(a_1,\ldots,a_n)$ be a partition of $2g-2$ with non-negative parts. For sufficiently large $r$, let $\mathcal{W}_{g; a_1, \dots, a_n}(r)=r^{g-1}W^r_{g,n}(a_1, \dots, a_n)$ be the resulting polynomial in $r$, and let $\overline{\mathcal{H}}_g(a_1, \dots, a_n)$ denote the closure of the locus of holomorphic differentials with zero orders $a_1,\ldots,a_n$. Holomorphic differential locus conjecture.

$$(-1)^g\mathcal{W}_{g; a_1, \dots, a_n}(0)=[\overline{\mathcal{H}}_g(a_1, \dots, a_n)]\in H^{2(g-1)}(\overline{\mathcal{M}}_{g,n}).$$

This predicts that the class of the compactified holomorphic-differential locus is obtained from the constant term of the polynomial extension of Witten's $r$-spin class. The claim has been proved by A. Sauvaget, so it is no longer open.