Most of it is stress related in my opinion. That can come from rough handling during collecting & shipping, poor water, a bad environment, and improper food among other things.
The proper diet of these (and many other cichlids) is one of the most misunderstood topics in the game. There has grown a myth that protein is a bad thing therefore these (and other) fish are vegetarians and will "bloat" if provided with anything other than veggie flakes. That's just not the truth considering that most veggie flakes are still basically fish meal.
Many to most of our favorite non-piscivorous CA cichlids are basically omnivorous. Lots of them spend most of the day grazing in the substrate, detritus, etc. in an effort to find suitable foods. As a result, they take in all kinds of materials: plants and algae, other fibrous substances, various micro-fauna, and small invertebrates. Basically, they are consuming lots of low-nutrition material mixed in with the less readily available snails, shrimps, etc.
Most fishkeepers who struggle with these fish feed them far too much meaty material and/or very high levels of indigestible protein. Bloodworms and the like are just terrible as a staple diet. A true veggie flake would be a better choice, but flakes quickly lose there nutritional value once in water. They don't provide a complete nutritional profile either. Pellets are better nutritionally since they hold their values usually until consumed, can more easily satisfy the appetites of large fish, and can be chosen to sink for more a more natural grazing-type feeding. They can also provide a measure of protein that a true veggie flake may lack.
However, not all pellets are created equal. You're looking for a highly digestible source of protein, not just any source of protein or a specifically high or low percentage. I know lots of people who have success feeding their beani, haits, various riverines, tropheus, and other "bloatable" fish NLS pellets. Some also find it wise to start out with the Thera-A type that includes added garlic as a mild anti-parasite ingredient until their delicate species start to settle in nicely.
Anything else you can do to eliminate stress is wise also. Growing up a group of beani or haits in a large tank with a ton of small non-aggressive dithers with help spread out aggression and reduce shyness. Of course, the water needs to be as close to perfect as possible too.