Magnesium Deficiency displays as a yellowing of the leaf tissue between the veins while the veins remain green. That plant kind of resembles it, but geez, thats not typically the classic look of magnesium deficiency. I mean it is, but it isn't. Magnesium if i recall is mobile, which means if the soil doesn't have it, it's going to pull it from the bottom of the plant to use it at the top. Thats why it shows up first in the lower half of the plant and not the top.
What throws me off a little is the droopy down curled edges, but that could be from a little over watering, and unrelated to the stripe issue. Man, i have to keep referencing that pic. If it was more yellow between the veins then it would be more evident that it's magnesium, But the damaged tissue isn't yellow, it's more of a flat light green.
Are you keeping your pH consistent, or are you being casual with it? You know, like 6.4 pH one nutrient/water mix, then the next water you mix a 5.8 pH and call it good? Not likely but have to ask anyway. pH fluctuation can cause a problem for plants and can even cause something that kinda resembles that, but again, not really.
Where it is on the plant means something as much as what is on the plant does.
I'm gonna say, reluctantly, that you can either buy a bottle of calmag, which will have Mg and start watering that in at the recommended dose with each watering and see if that halts the problem and perhaps reverses it. Calmag also has some N and some Ca, and FE. All of which are important in keeping your plants green. Or if you want to just try straight Magnesium you can Mix some epsom salts into your water and pH to 6.2 and water that in on your next watering. It won't take long for that to reverse if it's magnesium, but i don't feel confident that thats what it is. It just doesn't look like the classic magnesium deficiency look. Try the calmag or epsom salt watering at 6.2 pH. If it resolves, we were right! If it doesn't, then you know it's not likely Magnesium. Watering in either product won't harm anything anyways so there's no risk in trying those things.
Just remember to water when your pots feel light. Don't just go by a set schedule until you know how your plants are drinking. It's easy to over water a plant of that size. And if this is in happy frog or ocean forest like you mentioned in the DM, then those soils are very thick and dense and have high water holding capacity and low oxygen retention because they don't come with perlite. Last year i grew a big fuckin raspberry boogie in the back yard with ocean forest and i had to add perlite. I see your soil has perlite so you must have added some?
Well, thats my best guess, but i'm not confident that it's the correct one, but it's all i can figure. I'm gonna watch this question to see what other's conclude. It's very interesting.
Isn't it a bitch when deficiencies don't display in classic ways? Calcium is often like that. Shows up in lots of different ways.
