The eggs are all fertile, they are around a month old. I already got rid of that egg so it would basicly look like a normal egg bin with 1 missing in the middle
Then just that particular egg could have been infertile or there was something unknown that caused it to die. If you have them in a plastic container with a lid, sometimes drops of condensation can form and drip on the eggs, that can kill them.
Once in a while even good eggs can develop a tiny amount of mold and still survive, but not if they get very discolored and begin to collapse .