There can be a number of reasons for eggs not hatching. They may never have been fertilized, which could be the result of a physiological problem with one of the pair. Contaminants such as mercury or PCB (yes,PCB is still in our lakes in spite of the fact its use has been restricted for the past 20 or 30 years) can affect the eggs or the nesting behavior of the loons. Prolonged periods of being off the nest can also result in inviable eggs. This can be caused by other loons, humans, or black flies. Anything that can overheat or chill an egg will lessen the chance of hatching.
We may never know the exact cause of this nest failure, especially where we don’t know what the conditions were for the first ten days of incubation.