Is it the case that every Hamiltonian bipartite $3$-regular graph has a $4$-cycle?
My intuition says 'yes', because one can form such a graph by taking a $n$-cycle and adding a matching to it. When adding the matching, I think it should be inevitable to form a $4$-cycle eventually, either with edges from the $n$-cycle or with other edges of the matching added previously.
Any ideas on how to show this or how to provide a counterexample?