What is the problem?

High there you have magnesium deficiency. You can see this based on the yellowing at the edges of the leafs of the plants. This is probably due to too much light : more light more photosynthesis more magnesium required. So you can add magnesium also in the feed more regularly or as a spray (even during flower if you're brave enough) . But the best solution is to reduce as much as possible the light schedule for this plant so the problem stops spreading. Hope this helps ! 🚀

Looks like calcium. Calmag should fix it. If you're already using calmag, theres a chance that it's been locked out by too much bloom nutes.