Sounds like the very same issues I had with an indoor Northern Lite I had to cut down a month ago,,,dip your hands in the soild then stir up the soill a bit,,smell your hand and the soil,,if it smells bad then you may have root rot,,maybe from overwatering,,I tried to get an answer here but no one replied to my question, so I was left thinking it may be that reason,,,the soil was smelling awful and the plant looked stringy, weak, turned color and the leaves were very small and thin,,,I may be wrong with the answer but till someone tells you different,,check it out,,