Maybe it's too hot in the greenhouse or it needs some natural fertilizer or worm castings. I'm not sure where you are but I would put it outside, but in the shade close to or shaded by other plants to achieve humidity that way.

Or maybe you should loosen up some of the soil and dump it out, replacing it with rich, well drained soil. I grow my galangal in Dr Earths all purpose or vegetable soil in terracotta or fabric pots so they can breath. 3 gallon fabric pots, like smart pots, work very well.