Ep 418 AMA Episode - Which ETF with major tracking error were they referring to?

They talked about how a major index fund had significant tracking error and released a new product to address it, which ETF were they referring to?

Timestamp (24:32 - 26:24)

"we have now as a firm reached a scale and I think have enough of a reputation that we can go even to the biggest fund providers and say this is a problem... the fund provider actually corrected the mistake when I think was a mistake and created another product that's even structured I think in a better way."