The form you just received would have been a 2018 Form 1099-R, not a 2019 Form 1099-R. Code P on a 2018 Form 1099-R indicates that the amount in box 2a is taxable on your 2017 tax return. If the amount in box 2a is nonzero and not already reported on your 2017 tax return, you must amend your 2017 tax return to add it.
If you believe that the payer used code P on the 2018 Form 1099-R in error, contact the payer.
