Overwatering seems to be the problem. Overwatering and underwatering are very similar but the diference is that underwater make te leaves drop beacause they are very soft and squishy, in overwatering the leaves drop but they get stiff if you try to raise them because they are full of water. Just let the medium dryback until you feed them again.
You can lower the humidity and raise the temps to increase the transpirations rates so they dry the medium faster, but be careful to not increase the VPD too much.