Sorry you have had so much trouble with your Orps crops. So far I have only seen it in one of my Orps. Lots of things are genetic and crops are no different. I keep the crop bra handy all the time as once they get too stretched out and go pendulous they can quit on the bird. I believe it was a feed issue with my hen and switched her over to FF and or plain ground grains. She never had an issue after the switched and went 1 1/2 years crop problem free after this. Where as before it was a monthly event with her and the slow and sour crop.
I have only seen it in my blues, not my buffs, so it may be more prevalent in the blue/black/splash lines.