Leaves keep burning. Once they've fully grown (not so much...), they gradually burn from the tips, allowing the new leaves to develop before completely drying off. Reduced watering by half, and added a fan to keep the lot cooler. Not sure if the problem relates to the sun, or the soil (watering, nutrients, etc). Overall growth of the plant is half the shown by the other 6 plants of the lot.
A 10lt pot is on the way, expecting to transplant tuesday-wednesday.
One tip, Try not to overwater. In such a small pot it's easy to have this problem.
Also, in order for it to grow better, it would need a slightly larger pot.