Robin

We have a robin nesting quite low in one of our maple trees, she laid three beautiful turquoise eggs and was patiently sitting on them to hatch.
Three days ago the nest was abandoned, one egg was broken and half of it was on the ground.
Seems like there was nothing doing after sitting a week on them, I believe the frosty bitter weather and the low supply of sustaining food with the cold, delayed the seasonal progress.
She was very industrious building the nest and did all the right things, egg laying and trying to hatch out young but to no avail, no doubt she will start again when the weather warms up. The adults do sense when there's something not right.

Going off the description as the nest not been attacked

I wondered the same. Robins do have a reputation for abandoning nests which have been disturbed.

We have had the nests robbed by hawks or crows in years past, this time I'm not sure in this case, there was one egg broken and it may be that because there was no formed young in the egg, the robin female may have abandoned the nest as a result. The other two eggs weren't damaged.
Predators are always on the lookout for eggs or more so newly hatched young.

I haven't seen a single Robin this year...and not a English Robin, which are much nicer, in decades...

My Blue Birds are on their second brood, they have been nesting in that box for over 20 years..

I haven't found any nests, but there are dozens and dozens of baby Finches, Cardinals, Wrens, Chickadees etc in my garden and at the bird baths and feeders... Beautiful time of year.....

I have got pairs of long tail tits, blue tits, robins, blackbirds and wrens in my garden. I could watch them for hours flitting around finding food and nest building. I make sure my bird feeding station has lots of variety of food for them all including fat balls and dried meal worms as the blackbirds love them.