sorry, i have no answers, but as i was just going to make a thread about root kinking that can lead to a similar kind of stunting, i'll just join in and see what more experienced growers have to say. y best suggestion would be to CAREFULLY dig your plant up with a toothpick gently loosening the soil around it and very gently tuigging it until it comes free and then putting it deeper in the soil. root kinking was why my original super cali haze freebie was just a couple inches tall with a single gram "top cola", but that wasn't the worst i've seen. i once had some skunk bag seed that only made a TINY leaf pair smaller than a single pea. if anyone has any tips or tricks to avoid this problem, please do share. i'm guessing it's related to letting a plant start rooting in one orientation, then turning it when you transplant it. what i generally do is put my seed root facing down just below the soil surface, but maybe the root wants to curve around on it's own naturally. getting stunted plants is annoying though.
are you having THIS problem too? i think pushing it deeper should help if the plant starts adding taproots further up the stem.