Silkworms cocooning but not forming the silk egg??

[JubJubLizard]

Hi, I have a question about some silkworms that I’m waiting to cocoon. I have 3 that made their silk cocoons and now I have 2 that cocooned without making a silk egg? Has anyone ever seen this before or know what causes this? The housing conditions are exactly the same. Will they hatch into a moth if they never formed the silk egg :?: Thanks for any info :O)