Hi Fel, LED stuff is still relatively new..... just a thought that’s worth checking, what does mars say your recommended distance is? 3 feet away seems far from the top. Might not be though... but if you ask them they will tell you what the healthy range is for you to hover your light at. One other thing that others have touched on is watering, you might need to adjust based on feel if your in soil or another substrate. LED’s are a lower heat source and thus have less evaporation than some types. Meaning your water needs might be different from recommendations for a soil and HPS.
Over watering is a killer, might sound counter intuitive, but it’s true...Let it dry out before watering. It won’t fix your current leaves but it will help stabilize. It can get bone dry for a short time with out harm. (Just don’t leave em that way.)
Last thought, your closet.... how hot does it get? Air movement is something to think about but more over keep an eye on your temp. During the on period some small spaces can heat up even with a low of put from an LED. A quick thermo check is worth doing.