Plants show signs of heavy stress and/or deficiency, while i'm doing the same as always, and ph is stable at 6.3

It can happen when feeding to strong, ive seen it happen in flower and continued feeding with the same strength before flush but you could flush them and see if they start to yellow or it could get a nutrient lockout. If the nutrient line worked for awhile and then that started happening it might mean they didn't feed as strong.

Almost look like overwatering to me. Are you letting soil dry out between watering/feedings? I know Coco is usually able to just be watered constantly, but possibly the vermiculite is holding too much water in, would also explain your pot getting moldy, not being able to dry out. Dunno, just a thought. Overwatering would explain pot getting moldy, as well as all types of nutrient deficiency signs, droopy/twisting leaves. Try to get VPD in range, let pot dry out and see if they rebound. Good luck.

Looks like a boron deficiency, which would be rare. If your pH is solid, can move on to other causes. It's a rare "soilless/hydro" fertilizer nutrient line that doesn't include trace elements. You don't nee dmuch of these. It'll be fractions of a percent compared to the primary/secondary nutrients. N, K and Ca can ll interfere with availability of B, if their concentration is proportionally too high. N is generally safe in 120s I'd keep K 200ish or below and Ca should be 100+ and may vary with water used -- hard water will contain some Ca and Mg that might move the needle a bit. if crazy high in any of these, you might be locking out B. Also possibly a k-tox as that usually impacts the serated tips, but that progression in diary looks like boron. it started interveinal and grew to big ol necrotic patches of that color.

Thank you, for those good pictures! In my opion, this looks like a hefty deficency. The plant is eating up the stocks in the leafs, which is not good. On those leafs, this cant be reversed. When you grow on coco, you probably have not enough silica or calmag. Please add a big amount of calmag into the water! Emediately. When this helps, the plant will grow much better in the next week. When the plant has not enough of one thing, it cant grow proper, even when you give plenty of light and water.

Heavy nitrogen toxicity. Plain water if soil for 3 waterings, have 20% run off to wash salts out. Thats heavy really.

Looks like Your plants have too much nitrogen. Thats determined by the dark green colour and the down curled leaf tips. A few pix look like potassium deficiency with the rusty coloured necrosis on the tip and leaf edges. Some leaves look like nutrient burn. I haven't looked at your diary. I'm just going off the pix you've provided. One pic looks like under fed judging from the pale colour. But with different camera exposures and reactions to light it's hard to know. If this were happening in my garden my first line of defence is to flush my soil with 6.2 pH water. Get the salts washed out of there and reset your soil. Then allow for the soil to dry out and for your pots to feel light. Then resume feeding but at a reduced strength. I don't know what ppm your nutrient mixes are, but i wouldn't exceed 1200ppm. There's no need to.