Is it just the bottom ones, or all of them, and where is it, in a pot outside, in the ground outside, or under cover? And how tall is it currently?

Hi they were plug plants that I bought around Jan/feb that I've grown on so they're in 9cm pots in a fairly sheltered spot that gets the sun most of the day. One of them has a flowerspike thats about 6inches.

I don't know where you are in the country, but the most likely explanation is either cold (low temperatures) or drought.