It's either easy or hard to keep. Can't be both. Usually there is just one simple change that changes it from hard, to easy.
Like blue ribbon eels, for example. They were "hard" to keep (would not eat) because they would just stare at the food you gave them until they starved. Until in 2006 or so, when I discovered that all they need is a long tube to hide in; if they know that their long bodies can't be seen and thus eaten, then they have no problem grabbing silversides from you. All that was needed was a piece of pvc pipe longer than their body (3+ feet). Just google "my blue ribbon eel eats!".
So the blueberry gorgs are probably the same thing... some small parameter or food particle is missing.