Dead crab

I've had them for 2,5-3 months now.

I went to pick my fiance from a Halloween party a bit before 2 in the morning but everyone was fine when I checked on them before leaving, not 14 hours later I found one of them upside down on the ground, she had just molted a few days earlier and was very soft after I picked her corpse up.

She floated and smelled like dead seafood, now I'm getting worried if it was just after molt exhaustion that lead to her death or something else?

I checked on the others on their usual hides without disturbing them and saw them alive with a light.

They've gotten their normal food of shrimp-bloodworm flakes and veggies and haven't fought at all do far.