Nutrient deficiency?

No ones responded so yet so my 2 cents is calcium and or magnesium deficiency. Could be caused by too much residual salts in the medium, pH fluctuations, or just lack of the mag and or calcium. If they popped up that quick - personally I’m flushing that medium with pHd water at about 6 pH - run at least 2-3x the amount as the pot is. So if you’re in 2 gallon pots - run at least 4 gallons thru it. Check run off EC or PPM to see if it was indeed accumulating salt build up. Then add supplemental cal and mag to your feeds.. It’s a often good practice to flush your medium around transition to flower anyhow to push out residual veg nute salts out so they don’t cause issues with feeds in flower. Good luck