OK, so previous mention of 2017 was a typo.
I'm not aware of any way to cause TurboTax to include any of this distribution on line 4b of 2018 Form 1040 if the details of the Form 1099-R are entered accurately, so it seems that the nonzero amount on line 4b is coming from a Form 1099-R that you entered other than this code G Form 1099-R that has $0 in box 2a, or you entered a nonzero amount into box 2a of TurboTax's 1099-R form for this code G From 1099-R. Although it shouldn't make any difference, make sure that you didn't leave box 2a blank on TurboTax's form (make sure that the $0 was entered) and make sure that you entered code G in only one of the two box 7 boxes on TurboTax's form. As far as I know, a code G in box 7 and $0 in box 2a invariably results in none of this Form 1099-R being included on Form 1040 line 4b.
Examine the Pension and Annuities section of TurboTax's Form 1099-R Summary.
