King Snake Issues

My friend purchased a baby king snake from a pet store a while back. I checked her set up and it was decent. The king snake had a hide, water dish with fresh water, some kind of wood chips (almost like bark) and the heating was correct. She didn't even have the snake more than a few weeks and it died. She was really upset and almost didn't get another snake but a friend had a king snake he was looking for a home for. She took it. This one was a little bit older. Larger by maybe a few inches. I was providing her with frozen feeders and again, this one died. Heating and humidity were fine. High 80s. This second king snake regurgitated a meal a few days before he died.

Could it be the bedding? Could it be the set up (the set up seemed fine to me)? Could it be that the snake had an RI?

Set up sounds proper, could be the bedding, not likely but could be..Was the same unchanged bedding used ?? Is there some sort of residual toxic substance on the tank walls ?? Does the bedding have fertilizer in it ??
For one to have 2 North american colubrids die in that period of time says somethings wrong..??:snake: