Stein degree on log Calabi-Yau fibrations

We prove a conjecture proposed by the first author on boundedness of Stein degree of divisors on log Calabi-Yau fibrations. More precisely, for $d\in \mathbb{N}$ and $t\in (0,1]$, let $(X,B)\to Z$ be a log Calabi-Yau fibration of relative dimension $d$, and let $S$ be a horizontal$\mathrm{/}Z$ irreducible component of $B$ whose coefficient in $B$ is $\ge t$. We show that the number of irreducible components of a general fibre of $S\to Z$ is bounded from above depending only on $d,t$.