Soft yolks that break when trying to fry an egg?

[MasAhora]

Now and then I'll get a few eggs with a soft yolk. It's impossible to fry a sunny side up egg with them.
Any ideas why?
Usually my eggs have firm orange/yellow yolks and hard shells. I usually collect daily, sometimes every second day due to circumstances. It's baffling as I'll go weeks without a soft yolk and then find 3 or 4 when cooking (my flock varies from 30-50).

 

[ChickenCanoe]

I would imagine the issue is nutritional.
Yolks will break more readily when the eggs are older too.

 

[ChickenCanoe]

double post