Leafs losing Color, die off.

"should" -- the most useless word in the world, lol. "Should" doesn't matter when reality dictates otherwise. React to the plant, and sooner next time. Looks low on nitrogen based on the progression of the symptoms. Will most likely need more of other things as time goes on. This substrate is not living up to promises, clearly. Thoughts -- were you giving a ton of runoff? If so, you may have leached off nutes and shortened the time it could properly feed a plant. Or, it simply wasn't pre-charged with enough to supply a proper amount of nutrients to the plant and needs an adjustment in your soil recipe. Need more N released over time for sure. Possibly other things, but you'll have to wait and see the results to make educated guesses on that for next soil batch. If it was a pre-packaged substrate, it's no surprise that the advertising/marketing don't match reality. This is the norm in hoticulture. regardless of long-held beliefs, preconceived notions, or product marketing claims, always let the plant dictate reality. If it is deficient, that means the supply of that necessary molecule is not meeting demand. Nothing else matters beyond that. Taking notes of this stuff and when it happens can help you reformulate a better soil mix next time. It is possible for a soil to be nearly no-till for 4ish months, as it has been done before, but clearly not the case here. Trial and error over several grows will get you there. There will be speedbumps along the way and it will be a slow process unless you can get a sure-fire recipe from someone else, and even that will likely require tweaks.

Are you completely saturating your pots? Does the issue seem to get worse as the pots dry out? Autos should be in 5 gallon or bigger pots IMO. I've seen Autos start to experience root bound issues in 2 and 3 gallon pots during early flower.

I think the plant has probably used up whatevers in the soil and could use micros and bloom food.

Hey there when you water next time get a ph reading if the run off water that comes out the bottom of the pot. Garentee you have a soil ph problem mist likely the soil is to acid and just needs flush with plain tap water without adjusting ph. The ph levels are causing lockout so your plant is not getting the right amount of P an K. After flushing soil I would water the plant with whatever flowering nutrients you have don't over due it tring to make the plant come back I would give what the bottle says or even 1/2 the recommended dose cause after fixing the ph level the plant will suck up hats in the soil within 48 hrs the plant will look nice