Conjecture on the ML degree of rank-two 3 by n matrices

Let $\mathcal{V}_2$ denote the variety of $3 \times n$ matrices of rank at most $2$, with $n \geq 3$. ML-degree conjecture. The ML degree of $\mathcal{V}_2$ equals

$$2^{n+1}-6.$$

This conjecture concerns the number of complex critical points of the likelihood function for rank-constrained matrices. The supplied text gives no resolution status or further evidence beyond numerical experimentation.