Most likely too much pottassium and it lock out nitrogen.
Normally, I don't switch immediately. I mix half vegging fertilizer and half bloom fertilizer.
You can solve this problem by flushing. After this, use only 1/4 strenght of bloom nutes and step up. This particular strain might eat less than what the fertilizer manufacturer say how much to use.
Hey! It looks like Iron Chlorosis, it could be due to an improper pH when watering. I would need to know what nutrients you are using, how often you water, what pH you adjust it to, etc...
Looking forward to your response!