Snakes died - advice requested

[PanUzasny]

I hadn't seen my Valley garter for a while and went searching for him. I found him under something about 10 days ago, already partially dessicated and decomposing. I pulled him out and there was a little resistance, so I'm thinking he may have gotten stuck on part of the enclosure somehow (it's an Exo Terra). He was growing and doing well up to the point he went missing. His tank mate is doing fine as far as I can tell.

But today I found my Kingsnake dead. He hadn't eaten in about a month but I wasn't too concerned considering how long snakes can go without food. I've had him for two years and he'd been eating, defecating, and shedding just fine. Some of the mice had thawed in the freezer and I thought maybe that is why he wasn't eating, but maybe I fed him a bad mouse.

Both snakes were housed separately in bioactive setups with heat lamps for heat. The Kingsnake had a heated ledge to sit on as well.

Any advice is appreciated - I have two snakes still and want to make sure the same doesn't happen to them.