My guess is it's hormonal - now that they're laying the cockerel's advances are welcomed, so the girls are showing him some affection. Once it becomes a habit they'll likely return to doing it whenever his beard grows back enough for them to pick at again.Do you know why they do this and why it's never happened before? Did they only start grooming eachother now that they're (pretty much)full grown and laying eggs?
Some of my bearded birds (past and present) are messy eaters so the food bits in the beard are also attractive to flockmates.