To me that looks like a watering problem. Under water or over watering will cause this type of problem. Your medium looks to be to moist right now in photo at this stage in life me personally will water with spray bottle a few sprays around base and top of medium until a good root system develops. I don’t think it’s a humidity problem due to my area is always low in humidity you can check my video humidity was as low as 16% for a few days . My friend good luck to you 👌🏾