Was there anything between substrate and eggs? Crate? If the eggs were in direct contact with the moisture source they could've "drowned". If not then there was a humidity issue. Some plastic wrap between lid and tub could fix that. Lift one end by putting a book or block as riser could tilt the tub as to create an incline so any condensation would run to he edge avoiding any drips on the eggs.
With that being said, I'm sorry for your loss! That is a high percentage of egg to lose and hope you can correct the issue for next season! Keep your head up!