Low humidity in vegetarion is just slowing a growth speed and makes plant less potent in flower , but it not make plant leaves down like that.

Trust me, i tested in past runs a rooms with humidity arround 15% and that was coused naturaly by watering and if the feed is good and plant is healthy, your leaves will be up, not down like this.

In my option this may be lack of nutriens.

But i dont know how to fix it in your Living Soil, bcs i dont know what basic nutriens of NPK are missing.

Macro nutriens it could be, bcs they are just cousing that leave burn, but not that down possition like that.

Lets try to make your plants more healthy bro.