Hi,
This can often be caused by over breeding or breeding birds that are too young. Sun Conures should be at least 3 years old before allowing them to breed. The nest box should be removed after each clutch of eggs whether they hatch or not. If they hatch, you remove the box as soon as the chicks leave the nest. Once the chicks are eating on their own, you should separate them from the parents. The parents should be rested for about 6 months before letting them breed again. If this pair was not rested after the clutch that hatched, then that is your problem. Remove the box as soon as you are sure these eggs aren’t going to hatch, and rest the pair for 6 months before giving them the nest box again.
Thank you for asking Lafeber,
Brenda