Are there times the NaN error shows when there is not an error

[shell1]

We know NaN can mean the data isn't available or broken - and that makes sense to error.

A different case is this metric where Vanessa saw NaN she said it was a divide by zero.

https://experimenter.services.mozilla.com/nimbus/client-side-relevance-ranking-for-enhanced-firefox-suggest-phase-2/results/#wikipedia_enhanced_ctr

Ilana also had a case

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