the only time i had some die was when my tank wasn't doing so well, when i moved them they all did fine. one thing to look for would be aquarium iodine/ide, this helps them regrow their new exoskeleton faster and healthier. in my area it's impossible to find, but in others it's very easy. my ghost shrimp are actually very hardy shrimp. is there anything else in the tank w/ them b/c the shrimp need to hide while they are w/o their skeleton or else they are extremely vulnerable, which would be why u found ur where u did. there is a little skin around the antenae that comes off when they molt, same w/ their legs and tail too. mine are wonderful and if you have enough of them you could end up w/ little shrimp fry too! that's always exciting.
HTH