I agree it looks like
light burn.
The fact that's it happening most at the top of the plant near the lights is another sign it might be light burn. Light burn is caused by too high levels of light for too long and can happen even if it's cool, kind of like how skiers can still get sunburn even in freezing temperatures.
I've found it seems like it's easier to give plants light burn after week 6 or so of the flowering stage. I think it's partly that the plant has mostly stopped growing new leaves, so when overworked leaves turn yellow the plant doesn't immediately replace them, especially on the colas. I also think the plant is slowly creeping taller, and that's bringing it closer to the lights even if you don't notice it growing taller every day.
But luckily it's an easy fix if light burn is the cause. Raising the lights like you did should stop the yellowing from spreading, though it's important to realize the yellow leaves likely won't turn green again. Definitely don't try to overdose the plant with nutrients and especially nitrogen to "green it up" because it won't work but could deposit a chemical taste in the buds (and too much nitrogen in the flowering stage could prevent the plant buds from getting as big as they could).
Of course if you haven't been checking the pH, now would be a great time to start! The pH being too high or too low is the most common reason to see nutrient deficiencies

Managing the pH is almost like a supplement that makes plants grow faster and healthier!
Also, I just wanted to add that your buds and plants look great! The buds are very nicely developed for week 6!