are you a dutch grower? you use phillips bulbs and i don't see many mapito grows outside of holland, plus it looks like you have been playing hardstyle beats to your plants ! lol jk
i think it may be a sign they are getting slightly too much nitrogen at this critical stage of flower development, it is not a major problem and i think it will fix it's self in time
they look nice, what would you normally yield from your grow space?