Please Help, Plants Keep Stretching Buds Pull Apart

[gordonian]

So I have been having this problem on certain strains where the plant continues to stretch a little after week 4 and the buds pull apart. also some plants top buds never really form, the buds on the mid and lower plant are bigger than the tops. Not all strains in the room do this, and of the strains that do this not all the plants will. the worst offender is cheesecake pictured below. Any idea what could be causing this?
I run mills nutes,
EC1.5 at beginning of flower up to 1.9 by week 8.
PH 5.8-6.0
3 gallon coco pots
feed to 10% runoff, once plant feels 50% lighter feed agin usually 3 times a day
temp 80 humidity 70% to week 4 then drop temp to 75 and humidity to 55-60%.

 

[BudBogart]

How about time under light? Has the amount of time the plants are under light changed over past several weeks beyond normal shortening of daylight?
The stretching of the top and that three leaflet leaf at the top is what leads me to my guess.

 

[gordonian]

vegged at 18/6 and been at 12/12 for 4 1/2 weeks, also another symptom is the leave will point sup at more of an angle as the day goes on by the end of the day some will be pointing almost straight up

 

[BudBogart]

vegged at 18/6 and been at 12/12 for 4 1/2 weeks, also another symptom is the leave will point sup at more of an angle as the day goes on by the end of the day some will be pointing almost straight up

Using different lights, lower powered and/or too far away from the canopy? Leaves up at an angle reaching for the lights? I'm sure you'll get other suggestions, I'm stuck.

 

[Jfrezy]

Drop the humidity to 43% if positive

 

[Monster762]

Yeah I'm no pro but can you put lights closer without burn? If so do it. Usually reaching is the plant doing just that. Reaching for more light. Closer is more intense light and should stop the reaching. I'd say they want more light.

 

[DemonTrich]

Looks like a reveg to me

and possibly russet or broad mites due to what that looks like in the pic.

 

[gordonian]

So for the most part its the tallest plants that have stretched are the ones with the leaves pointing straight up. The tallest plants are about 3 feet away from the lights, which are gravitas btw. There are shorter plants of the same stain that the leaves are perfectly normal. Def no broads or russets in there, I have had them before.