Phenotype expression , exacerbated further by the ruderalis genetics. You want picture perfect similarity, run clones.
This is why autos lose a massive amount of points for me personally.. the one on the left is gonna finish way before the other one. My strawberry pie auto went 105 days..
If you want consistency, get some fem photos, pop a few, find one with desirable traits and make a mother, take cuts and do runs from those.