This mould just appeared on main stem plants near finish, week 8 flower. this particular plant had growth probs but i dont think it is connected to that.
Is this one or two plants? I can't see much of anything in the first two pics.
Last 3 look like mold or a stem canker. I'd keep temp and humidity in range and put a fan blowing through the crown. If it's mold-like, wipe it off with vinegar on a cloth.