I think this is a micronutrient deficiency/lockout due to underwatering, underfeeding and PH imbalance. From my research it looks like Iron or sulphur. I fed them with Compost tea and more dry amendments, they seem to have perked up since.
looks like a sulfur deficiency. during flower is when it's needed and when you have monster plants they need even more . Adding sulfur is always a good idea anyway it's really important for terpenes and everyone loves terpenes. Hope this helps 🚀