Normally iam not confused about loosing and yellowing leaves at the bottom, but i had 2 similar plants and one showed it, so i found i had a manganese defiency due problems in the soil . I flushed my lady properly, and gave her some fertiliser ( most contain manganese). it never showed up again until now. its no serious thing, if your grow stops the next 4 weeks. I had to go longer and had to react.