how wet is your soil? looks like a root problem mine started doing that. Do you smell a funny odor? if you do or don't if you can handle lifting and looking at the roots if brown i would gently trim them off. (not the leaves just yet) put back in slightly dry soil? and just mist the medium you put them pack in and wait to water then water down stem with less water. Of course i don't know much and I'm just guessing based on my experiences. Check some of the guides here on RIU hell I probably should look some more myself but trial and error is the only real teacher good luck and hope my response gave you some help.