Why does Bitcoin Cash Price Diverge from Index Price?

[Swagtoshi]

As the price of Bitcoin Cash falls, the gap between the futures price and the index price increases. What cause this phenomenon?

In the past, the futures price followed the index price closely, usually a bit higher than the index price. Any dip below the index price was temporary and was quickly corrected. However, the price of the future is below the index price for an extended time. What are some explanations? Does the hard fork contribute to this?