I suspect your don't have enough light intensity for optimal conditions or that it's a light penetration/competition issue based on density of foliage. Legginess is a function of light and heat. Transplant timing would not be expected to affect it. Plants will often start to cannibalize and drop lower leaves with material light intensity differences between higher and lower leaves, particularly in warm conditions. When the plants form a tighter canopy toward the tops, this further decreases the light to the lower leaves, exacerbating the effect.
A "greenhouse" effect can also result, which may result in higher humidity and transpiration challenges for the plants. There appear to be signs of this effect in the foliage. I have this to a degree in my grow because I have many plants in an enclosed area. I have to monitor it and open/close the door and/or use the fan to maintain warmth without letting the environmental conditions have too much of a negative effect on growth. Some plants are affected more than others may not always look pretty, but mine are going outside so I just need to get them there healthy.
It's also possible that inconsistent or over watering and availability of nutrients could play a part here, but I don't have the impression that's the issue - or at the least, not the main issue.