There was a bug in 2019 TurboTax that was causing duplication of certain taxable amounts on Form 1040 line 4d, usually triggered by a code H Form 1099-R also being present which was not the first Form 1099-R entered. This bug was corrected in release R14.
Correcting certain inaccurate information provided in earlier posts in this thread, code B does NOT itself imply a nontaxable distribution. Box 2a can indeed have a nonzero taxable amount properly shown in box 2a of a code B Form 1099-R. A distribution from a Roth 401(k) is only nontaxable if the amount in the account is less than what was original contributed to the account (basis greater that or equal to the account balance) or if the distribution is a qualified distribution because the recipient of the distribution is over age 59½ (or qualifies as disabled) and the distribution occurred at least 5 years after the beginning of the year that the designated Roth account was established.
Unlike a distribution from a Roth IRA, there is no box-7 code to indicate a qualified distribution from a Roth 401(k). A qualified distribution is indicated by the code B Form 1099-R not being accompanied by code 1 or code 2 in box 7 showing in box 11 a year of first designated Roth contribution more than 5 years prior to the year of the Form 1099-R.
