Deformed pupae

I had this Actias luna caterpillar doing fine up until it became a pupa.
I could see it inside the cocoon for a few days wiggling around and I thought it was alright.
I opened it up because I wanted to sex it and then I flip it over and there's feet. It's still alive too, which is really unsettling, but it will probably die.
This wouldn't be the first time that I've had some deformed pupae happen to me.
I also attached a photo of a monarch chrysalis I once had that became really deformed, I would see inside of it and it was also alive.
Maybe it's natural, but I want to know why this happens, is it something I did?