Autoflower strains

Short answer: yes, yellowing can appear on your leaves at any point of your growth, be it vegetative stage or flower stage. It always means that something is wrong and and can have many reasons; if you take the time to really analyze the symptoms you can tell what's going wrong. Looking at your photos it seems that the Auto Sweet skunk is the most affected and that the yellowing is at the top of newer growth, not the older foliage, so it's not Nitrogen deficiency. You might have not noticed, but along with the top leaves been yellow they also have really thin blades. I believe what you are seeing is an excess of P-K, both excesses of phosphorous and/or potassium will make the newer leaves turn yellow and develop really thin blades; also they will cause several lockouts like calcium, magnesium, iron and zinc. I would measure the strength of your feeding (EC/PPM) and dial back or stop altogether with the PK13/14