What are the units corresponding to the numbers in the nutrient columns?
My guess is that the plant would have liked the nutrient mix at a higher concentration, especially during the preflower stretch and for the first couple of weeks of flower after that. That is when the plant is the hungriest during its life cycle.
Also, switching to a higher P ratio in the nute mix too early will cause N deficiency in the plant.
Also, because you are using RO water, the CalMag should be fed at a higher ratio than indicated on the chart.
Flushing the plant with only RO water starved it, so it consumed resources stored in the existing plant matter to sustain new growth.
I didn’t see what light you are using, but if you are pushing it with strong light and warm temps, it is even more hungry.
I use tap water that comes out of the faucet at around 200ppm. At the heaviest, from befinning of preflower stretch and for the following 3 to 4 weeks I feed in the range of 1000ppm to 1200ppm. I supplement CalMag with Botanicare CalMag+ at a rate of 2mL/gal. I use GH Maxi dry nutes. I also supplement with BluePlanet EasyWeed at 1/8 tsp/gal. I feed only high N veg MaxiGro through the end of preflower stretch and the beginning of bud development. I transition to high P MaxiBloom over the course of a few weeks, and I feed with only MaxiBloom for the final 2 weeks before chop. Bloom nutes have way more P in them than the plant can really make use of.