A note on stability shifting for the Muskat problem II: Stable to Unstable and back to Stable

In this note, we show that there exist solutions of the Muskat problem which shift stability regimes in the following sense: they start stable, then become unstable, and finally return back to the stable regime. This proves existence of double stability shifting in the direction opposite to the one shown in [C\'ordoba, G\'omez-Serrano, Zlato\v{s}, A note on stability shifting for the Muskat problem. Phil. Trans. Roy. Soc. A, 373 (20140278), 2015]