Failed robin nest

Good morning all. 

This year we put up a new camera box, specifically for robins and were delighted when a pair moved in after just a few days. They built a nest, hatched 5 chicks and then things started going wrong. After a week or so there were only 2 left and then they disappeared too, although I did observe one on the edge about to jump. I don’t know whether he survived.

After another couple of weeks I noticed Mrs Robin back on the nest brooding 3 new eggs. After about 10 days of brooding I noticed her behaving strangely one morning, scrabbling around in the bottom of the nest as if looking for something then she just flew off and hasn’t been seen since. Two of the eggs are now on the ledge at the side of the nest. The photo isn’t very clear but the bottom of the nest is about 3”deep so that ledge is quite high for a bird to push the eggs up there. 

Is this unusual behaviour? Could Mrs Robin move the eggs up there herself? And why?