This is a bit odd too. You said, 99% is caused by poor husbandry. So why mention that one percent could be spontainous.
I would think that is something fails in your care, you are responsible. End of that story.
The point here is, the one I responded too, said, its going to happen because we cannot copy nature, not even zoos can. This is the problem.
The standard nesting techiques that are used for colubrids, are Terrible. Marginal at best.
As far as I can tell, its the box in a box, syndrone. That is, people keep snakes in mostly small boxes, then think the nest must go inside the already small box. This is wrong.
Reptiles nests are very critical to recruitment. They are not small. They cannot be. The reason is simple, they must have mass to maintain both temps and humidity for a couple months.
This is what snakes are looking for. Something down or in, with stable humidity and stable temps.
Yes I know, up north some snakes nest under little stones. Well in most cases, we aint up north and do not have those conditions.
Back to the point, nesting issues can easily be avoided. But most people live in a bandaid world, so they would rather put a bandaid on it, then fix the problem. After all, if there was no problem, there would be no bandaids.