Appreciate the answers but it isn't likely to be either of those things. Both plants split their main stems as seedlings around week 2 inside a propagator with no pest damage to any of the plants. During this time I never gave them any seaweed supplements or other type of auxins, only the small doses of GH Rapidstart that they all received. I've also grown other plants with added seaweed - cannabis and not - without any weird growth or unexpected behaviors such ass loss of apical dominance.
Tried posting another question but it doesn't seem to want to let me, but hopefully I'll solve this mystery one day.