I've had lot's of practice with FF. Burning isn't an issue for me but the salts will build up if you don't water & flush like they want. I try for 25% of the water out the bottom every time or the leaves will get skinny.
Looks like a flush would do you good. When the salts build up the leaves don't open up like in your pix. All you have to do is get the salts out while keeping your nute level up and not watering until it's time........
When I get it right i'll let you know.
The roots are everything, worth every minute you invest reading up on. Your healthy plants need considerable energy to finish. Leaves = roots = flower till it's capped out.
Wow nice job. My vote is roots. Some pix look like water damage, huge pots & you haven't mentioned roots yet. This thread could have been mine last year.
I see nothing. The herm stuff always has a little tiny stem between it & the plant. If whatever you are looking at is sitting in contact with the plant then you're golden.
Have a cookie!
If they needed water then the leaves are turning from too much nute. If you haven't added nutes yet, then it's coming from the soil. I bet one good flush with plain water will show improvement.
Don't see any light issues, I still think they look awsome.