This is not a perfect example of what you seek, but one could argue that Francisco Santos' counterexample to the Hirsch Conjecture has reinvigorated research on polytope diameter bounds. The Hirsch Conjecture says that in $\mathbb{R}^d$, an $n$-facet polytope has diameter at most $n-d$. Santos constructed an $86$-facet counterexample in $\mathbb{R}^{43}$.

In some sense, this was the impetus for the polymath_3 project on the polynomial Hirsch Conjecture. Progress from polymath_3 and other advances are summarized in this paper:

Santos, Francisco. "Recent progress on the combinatorial diameter of polytopes and simplicial complexes." Top 21, no. 3 (2013): 426-460. (Springer link to HTML paper.)