My guess is them going into flower they need more fertilizer and also make sure your pH in the rootzone is around 6.0-6.2 with flora/maxi nutrients during bloom especially, shoot for the 5.8-6.0 range during veg. Remember in mid/late flower to adjust your feed with stretch being over with, they usually don't eat as much once the plant is in mid/late flower and you risk overfeeding.
You need to closely monitor pH as it literally regulates if your plants eat or not, I had some plants in bloom go yellow looking and I had to not only boost the amount of fertilizer but also raise my pH quite a lot to get the rootzone up there, as you dump fertilizer into the pots the pH can go acidic over time in the rootzone itself, especially with limited runoff which I don't have an issue with, but many do.
In my case my runoff was 5.8 pH (orange with pH drops/strips) and so I gave a heavy feeding at 7 pH (dark green) to get my rootzone to around 6. Sometimes it might take 2-3 high pH feedings to get the rootzone wher you want it. Just adjusting the solution to 6.0 then feeding isn't going to correct an acidic rootzone, it will simply drop in pH once it absorbs into the roots with the other acids.
Once your pH is dialed you will see your growth explode like never before and realize how important it is.