Here's a question with the answer. I e-filed until 2016 then filed by mail in 2017. Since that time I've been unable to e-file. My returns were rejected with the infamous IND-031-034 error of bad 5 digit PIN or AGI. The AGI and 2016 PIN were correct, verified by IRS transcript and my records.
What finally worked this tax year (2020) was using $0 for the AGI with the 2016 PIN. My theory is that the IRS computers were looking for my 2016 AGI (the last year I was able to e-file successfully and *not* the 2019 AGI as stated in the instructions).
I can't prove this because I successfully filed with AGI $0.