Maximal green sequences are studied in many papers. For example, [Maximal Green Sequences for Cluster Algebras Associated to the n-Torus](https://arxiv.org/abs/1412.3713) by Eric Bucher, [On Maximal Green Sequences](https://arxiv.org/abs/1205.2050) by Thomas Brüstle, Grégoire Dupont, Matthieu Pérotin, [Minimal length maximal green sequences](https://arxiv.org/abs/1702.07313) by Alexander Garver, Thomas McConville, Khrystyna Serhiyenko, [Maximal green sequences for quivers of finite mutation type](https://arxiv.org/abs/1606.03799) by Matthew R. Mills, [Maximal Green Sequences of Exceptional Finite Mutation Type Quivers](https://arxiv.org/abs/1406.1072) by Ahmet I. Seven. 

Which cluster algebras where the existence of maximal green sequences is still unknown?

Thank you very much.