Most likely due to switching to bloom nutrients way too early in the flowering cycle.
Cannabis still needs adequate nitrogen in early flower to help with the stretch and to transition to the flowering phase.
Switching to bloom as soon as the first pre-flowers appear often leads to horrible yellow plants at maturity, leading to harvesting unhealthy, almost dead flowers with no smell and awful taste.
What I recommend is to continue with grow nutrients for the first two weeks of pre-flowering, then go to half grow and half bloom for the following two weeks and only then switch to straight bloom nutrients.
This seems to produce the biggest and healthiest flowers on plants that don't exhaust themselves and end up a sickly yellow colour at harvest time.
I have been doing this for thirty odd years and it works well for me.
I think mouse got out of the wrong side of the bed this morning!