Yeah, don't worry about it... It's a natural *survival of the fittest* thing- you'll always get those born with defects or susceptibility to problems. The *runts of the litter*. Most of these are selected against by the first or second moult- then if they die, it's 'more' likely that it will be due to something you're doing wrong
When a large amount of nymphs hatch from an ooth often many of them die. That is one reason many species lay hundreds of eggs. So that at least some of them survive to adulthood.