Why do leaves get yellow and die?

I find this happens when over watering has been a thing and some root rot or some weird growth in the root zones is happening. Might need to amend with more perlite next time or dial in your watering habits. The yellowing of the lower older growth also does seem like it is not getting enough N. But the leaves should not be burning, twisting and collapsing into a thin folded blade. if all it was is N they just yellow nothing else. that is a key indicator to me its root issues maybe rot. Some of the spotting does look like PH but I would expect to see that on the whole plant not just some of the lower leaves.

looks like normal, because the are not getting direct light (: would not worry! adjust ph to 6.4 and feed some N 🌱💚

Hello mate, you have an issue with Ca/Mg caused by a pH fluctuation or a misfeeding of Calmag product. The first cause is often link to the rate of Ca/Mg in the water used to watering the plant, if you use organic feeding you must have the rigth rate of these nutrient that is 3/1 or 4/1. Good luck and happy journey!

Yes, I believe she's hungry and resorting to starting to use up her mobile nutrients stored in the leaf tissue. This is normal and slightly early to see it but not unheard of. A little liquid kelp is good in bloom and may help boost some n too. They still need some N during flower just don't give crazy amounts to avoid grassy flavor. or any all-purpose bloom fert should have some N as well in the right ratio. if not in flower I would say feeed some fish hydroylasate.

Looks like she didn't have enough nitrogen going into flower, usually the lower leaves will do this. Your using nutes now so it's probably something lacking a few weeks back.