Excel Formula to regression fit Cubic polynomial

[vsennak]

Hi,

I am using the following function to do the curve fitting.

=INDEX(LINEST($G9:$G22,$F9:$F22^{1,2,3}),1,1)

It works most times but not for certain data.
And there is a mismatch between the trendline (polynomial cubic) and the values returned by the function for this data set.

Attached is a sample data set.
Also, whenever this happens, the C term or coefficient of X term goes to zero from function calculation.

Any pointers to the issue, most welcome.

Thank you in advance.