This is completely different from being egg bound. Sometimes you can fix egg binding since the egg is in the oviduct and maybe can be eased out, but internal laying is something that is beyond our help. It is genetic/hormone-related and most prevalent in common hatchery breeds like the RIR, Production Red, Sex links, Wyandottes, Buff Orpingtons, Rocks, just any of the most common/popular ones sold by the big hatcheries. Ones no one expects to be an egg-a-day layer for her entire first two years would most likely do better, like Brahmas. My two, though hatchery stock, have so far been trouble free.
Pick birds who are not high production type breeds like are the most common hatchery birds. That is no guarantee, but it will probably plague your flock less often buying from a breeder rather than a hatchery.
Signs. Hmm. Going on the nest often, but producing no egg, straining on the nest, then later, just ignoring the nest. Finally, the bird will begin to lose weight drastically even though she is eating well. Her abdomen may not even be swollen--many of mine were not, so there was no way to palpate anything amiss, like we could with Olivia. Then they become very weak and eventually will die if you don't euthanize them. I've just seen it so much I am suspicious when a hen goes to the nest but gets off without laying. I spot check abdomens from time to time now, but if the bird isn't holding fluid, that won't help much in diagnosis.
Tim, not sure exactly what you mean by mushy. The abdomen shouldn't be hard to the touch at all. If it is, like with the Del I lost, you know something is terribly wrong. If filling with fluid, the abdomen will become bulbous and like a water balloon filling up in the sink.