There's a number of reasons for squished eggs in the nest at hatch.
The mother tying to assist a duckling.
Drake mating the hen on the nest.
The hen stepping on the eggs when there isn't enough nest padding
An overweight hen who is lying on the eggs with all her weight.
Too much interference at hatch time with a duck who is not tame.
A nervous inexperienced hen.
I have had all these happen over the years with many species of birds. After reading your post and looking at the egg those marked in red are the strongest possible reasons.
I have found that for the best luck in hatching, use a covered nest to avoid unwanted male attention, an abundance of soft nest material to keep eggs from being crushed when stepped on, a few hard dummy eggs to hold the hen up so her weight doesn't crush the eggs, and restraining ones self from disturbing the nest when eggs are hatching. I have a really hard time with the last one even though I know the risk and have had upset hens crush eggs.