plants in 12/12 but not flowering

Hi, I started flowering about a month ago and of my 4 plants 3 of them have nice colas going on, but 1 of them ujst has a few white pistils and thats it. The lone plant is more developed then the others as of it has been vegging for the past 3 weeks and only just figured out to flower, what could cause this? cause now one plant willl be harvested a week later.

did u have clones or seeds it is a bit strange u should put up pics.

this might be a different strain then the others..