Some strains are simply unstable / more random than others. I'll start my explanation with a little rant I have a Devon Rex cat. He is white all over except his nose, paws, and ears. His mum is brown all over, his dad is 2 shades of brown. All siblings look just like his parents. His inexplicable colour and patterns come from latent genes past down from his grand parents or even great grand parents. So back to plants: same thing can happen. Sometimes a strain is the first generation of 2 different strains crossed, so in one batch of seeds there can be numerous different combinations of both of those parents. Maybe some will turn out just like the mum, sometimes others may be just like the day, others again may be something right down the middle. Etc. But.... how stable are said parents? Were they first generation crosses in themselves? If so, it's not really Plant 1 x Plant 2, it's P1 x P2 x P3 x P4, so possibly every combination of those plants expressed between one batch of seeds. Going back to the cat example, maybe while the mum cat was brown, perhaps she was the odd one out in her own litter and her siblings were white... I don't actually know the answer to flesh out this example more, but yeah just consider that example Last, I'll give the example of Sensi Seeds Ruderalis Skunk. In the product description, it says only 50% of plants will be auto, with the rest responding to photo period. So just as different strains can have a variety of parent traits between seeds, such as height, smell, etc, for auto's it can also be a mix of if it really is an auto or not. A first generation cross between a photoperiod and an Auto will likely produce a very mixed batch where you won't know if it's auto or not from seed to seed.