"Now my previous employment is correcting the 1099R with code J."
That makes no sense. I don't see how your previous employer can legitimately generate a Form 1099-R with code J. Code J is only permitted to be used for distributions from a Roth IRA and a Roth IRA custodian who can use code J, T or Q can only be a bank or an IRS-approved non-bank custodian. The original Form 1099-R with code B and your description that the distribution from the Roth account was in conjunction with the distribution from the traditional account in the 401(k) suggests that the distribution was not from a Roth IRA but was instead from a designated Roth account in the 401(k). As such, the code B on the original Form 1099-R would be correct, although it's unknown whether they reported the correct amounts in boxes 2a and 5. A correct code-B Form 1099-R would have the taxable amount in box 2a, the nontaxable amount in box 5, and these would sum to the amount in box 1.
Even if the distribution was from a Roth IRA, code J would still make no sense. Code J means a distribution made to you before you had reached age 59½.
Under no circumstances can code J be correct for this distribution. I suspect that the other information that you have received is erroneous because these providing the information have relied on your seemingly erroneous assertion that the distribution was from a Roth IRA.
