I'm gonna guess nutrient lockout from to much food.( leaf tips curl down like that usually from nitrogen toxicity ) Another sign is the dark green shiny leaves.
Got a EC/PPM pen if not get one as this will help you figure out if your over/under feeding.
You test your feed and compare it to the runoff to see if its over feeding. It should be close to the same EC/PPM going in.
What are you feeding, how much and how often? Synthetic or organic nutrients. What medium, soil or coco.
When you water do you water until you get runoff to avoid salt buildups?
If your feeding with your watering(not top dressing) and synthetic(not organic) then I would do a flush and adjust your feed to be less.
**If your organic then you can wash away the good microbes in the medium or if you top feed then you can release more nutrients which can make things worse.
measure out 3x your pot size of water and adjust the PH to what it should be in your medium.
Run PH water through until you get a minor runoff. Wait 10 min to soften any salt buildup then run the rest of PH water through.
Now that you have flushed out all/some of the nutrient buildup you want to do a regular feed right away to get the correct level of nutrients back in the medium.