Correct, nitrogen deficiency from switching to bloom nutrients too early.
Cannabis still needs adequate nitrogen in early flower.
I continue with grow nutrients for the first two weeks of flowering, then change to half grow and half bloom for the next 2-3 weeks (depending on flowering speed), before changing again to straight bloom nutrients through until maturity.
This seems to produce the biggest blooms on plants that don't exhaust themselves and end up a sickly yellow colour by harvest time.
Have been doing this for close to 30 years now and it certainly works for me!