On the Albanese morphism of varieties with Frobenius stable Kodaira dimension zero

We show that in positive characteristic, the Albanese morphism of normal proper varieties $X$ with ${\kappa }_S(X,{\omega }_X)=0$ is separable, surjective, has connected fibers, and the generic fiber $F$ also satisfies $\kappa (F,{\omega }_F)=0$. As a corollary, we deduce a new case of Iitaka’s subadditivity conjecture for fibrations over abelian varieties, when the generic fiber has non-nilpotent Hasse-Witt matrix.