This is NOT a distribution from a Roth IRA. It is a distribution from a designated Roth account in an employer plan like a 401(k).
The taxable amount of this distribution is the amount in box 2a of this Form 1099-R, $0.
"The IRS wants to tax the distribution saying they can't determine if the distribution is a pension or an annuity."
It makes no sense that the IRS would question this distribution. The code B and the amount shown in box 2a tells the IRS everything they need to know about this distribution to determine that it is nontaxable income. Apparently whoever at the IRS questioned this distribution is inexperienced or inadequately trained. The type of investment that was held in the designated Roth account is irrelevant to the tax treatment.
