We describe the normal stable surfaces with K²=2pg-3 and pg>14 whose only non canonical singularity is a cyclic quotient singularity of type 1/4k (1, 2k-1) and the corresponding locus D inside the KSBA moduli space of stable surfaces. More precisely, we show that: (1) a general point of any irreducible component of D corresponds to a surface with a singularity of type 1/4 (1, 1), (2) the closure of D is a divisor contained in the closure of the Gieseker moduli space of canonical models of surfaces with K²=2pg-3 and intersects all the components of such closure, and (3) the KSBA moduli space is smooth at a general point of D. In addition, we show that D has 1 or 2 irreducible components, depending on the residue class of pg modulo 4.
Ciliberto et al. (Sat,) studied this question.