If it's missing in TWS, then there's no API issue (at least not on the last mile).
I doubt it wasn't available on the market, so only reasonable explanation is that the gamma was so high it hit some ceiling in TWS.
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Out of curiosity, did you have the checkbox for local calculations selected or not? Not sure if that is the problem or not so you might want to test (including re-launching TWS after changing it).
Configuration > Volatility and Analytics > Use Local PC to calculate Bid / Ask IV
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Please let us know here of your results.
