Great tit nest

Hi, we've had a Great Tit nest in our garden for the first time this year. Approx 3-4 chicks were seen fledging. We've now removed the bird box they used to clean out & found x5 very dead crispy chicks plus x1 unfertilised egg. Is this normal to have so many fatalities? Is it normal that the dead chicks were not removed from the nest? Thanks for any feedback :-)