at the end of season the air is cooler, colder, with less soil web activity, less insect frass, less poop, slower composting, etc...all triggers for a plant to finish its season. all my garden veggies do it, outdoor mj, trees, herbs. its beautiful.
but seeing as you're indoors none of those things are at play, so it appears one or more resources are not being taken in by your plant at mid flower, maybe a natural reduction at this time of N? probably wont be an issue. Think of what changes have been made most recently. Consider your nutrient line up, feeding habits, instructions, additional additives, ph as a possible culprit. My leaves indoors sometimes change in their last couple weeks of life.
I think your plants look great in their nice space, you've brought them this far I bet you have no worries to finish