Let $G$ be a finite group and $H$ a subgroup.
Let $\mathcal{L}(H \subset G )$ be the lattice of intermediate subgroups between $H$ and $G$.
An intermediate subgroup $H \subset K \subset G$ is a normal intermediate subgroup if $HgK = KgH$, $\forall g \in G$
Suppose that $\mathcal{L}(H \subset G ) \sim B_3$, as follows:
Let $K_i$ ($i=1,2,3$) be the minimal overgroups of $H$.
Question: Is there $i$ such that $K_i$ is a normal intermediate subgroup of $(H \subset G )$ ?
Remark: I've checked it's true by GAP, for $\vert G \vert <144$, except $64, 96, 128$.
No, the example of @ahulpke here is a counterexample:
First, the program IsNormalIntermediate is the following:
Next, the couterexample of @ahulpke is:
because the lattice is equivalent to $B_3$:
and the $K_i$ $(i=1,2,3)$ are not normal intermediate:
Remark: The others intermediate subgroups are also not normal intermediate: