Will a plant not flower and bud properly if too cold at night?

I have 5 plants in grow area up in open attic. I have tried my best to enclose the 6x9 area to stay warm but it still gets too cold at night when light shuts off. All 5 are in flowering stage but only two of them are growing bud. The other 3 only continue to have hairs now for the past 5 weeks. I have put a small heater on at night but it still gets too cold. If I bring the three down at night into the warmth, shouldnt they continue to flower and bud like they should? They have just stayed that way for weeks. The other two of same strain are doing fine. Don't get why two would do fine and the other three remain with just hairs.

how cold is cold? are they the same strain? a better way to heat them over a electric heater that burn crazy amounts of power not
to mention a fire hazard, would be to run a small 4in fan and duct it from your inside house temp air up to the plant, just a idea

i'm not familiar with what is "too cold" for flowering. right now my temps hit the low 50s at night in the closet and about 75 during peak of lights on, and so far so good. in general though cold temps do stunt growth and can contribute to nute lockout. if controlling the air temp isn't working you could try a heating pad to keep your medium and roots warm. should use less electricity and be more effective. how cold is it in there?

Low 50's and phosphorous absorption is hindered. Plants typically turn purple as a result. It helps to provide more water soluble P, and foliar feeding can help also.

Not a big deal if it is only during dark hours, but prolonged cold could certainly lead to problems.

Just a stoner's thought..do you have a bathroom ceiling fan? Where does that go? Could it be routed to your grow to vent in warm air at night?