Nielsen's obstruction conjecture for second-order B-spline Gabor frames

Let $Q_2=Q_1*Q_1$, where $Q_1(x):=\chi_{[-1/2,1/2]}(x)$, and let $\mathcal{G}(Q_2,a,b)$ denote the associated Gabor system. Nielsen's conjecture. The Gabor system $\mathcal{G}(Q_2,a,b)$ is not a frame for

$$a=\dfrac{1}{2m},\qquad b=\dfrac{2k+1}{2},\qquad k,m\in\mathbb{N},\quad k>m,\quad ab<1,\quad \gcd(4m,2k+1)=1.$$

This is a specific obstruction to the frame property of the second-order B-spline, and the source states that the conjecture is proved in the paper.