Hiya pal 👍, different seeds different genetics, different stress tolerances, slighy different nutrient profiles, who knows could just be lackluster genetics next to 2 vigorous genetics or maybe she had problem breaking the seed shell.
68F 70RH% Anything would have mild discomfort growing in that. Transpiration is dependent on latent heat to perform endothermic cooling, not terrible but the cold is slowing everything down grinding down what little growth is happening maybe she is in the pot closest to cold air intake? 🤔
Sometimes even that little extra few degree or extra airflow over time accumulate to different responses. Defo heat things up a little. I personally wouldnt put too much thought into it, sometimes you just get a dud comparatively, if they all looked same as the small one then there would not be a issue.
Best of luck. Yummy gelato.