Head not forming right

pic's of other ones to show the size diff in them.
It seams to be only one just not doing anything, very tight small and pretty much for the main cola its not showing any signs of growing anymore. any idea's?
Set up is 600 watt HPS with large avenger shade. room temp is 25 degs C good air flow and outflow, They are in soil which is testing good with PH watering 5.5- 5-9 for PH also.
Its the 1st time I have come across slowing down of flowering.
pic 1 and pic2 is of the plant im talking about

How old are they?

I had 4 veg for 6 weeks and that one that's not forming has been in flowering stage for 3 weeks now.
hopefully this photo will show of what the other one's look like instead of that sorry state of one which im thinking of throwing out

sort of looks like its revegging.....

That's what a mate has said to, I am putting her at the back there is no light leaks or any other type of leaks in there, she seams to be the only one doing this, Hopefully she works out what she wants to do over the next week as shes been on 12/12 now for 3 weeks and she should look like that other one, nice and forming, Will give her a week to work out what she wants to do, Or she might be getting thrown out

Rosetting, trim it off

Peek at the roots. I've seen fusarium or other mildews on the roots cause that in flowering.