If you've read any of these questions and comments then you know that many of us experienced this issue. I too filed my 2019 return in January this year. Obviously very late. I finished my 2020 return last night and it was initially rejected. I reached out to a Turbo Tax rep who told me that even though my AGI number is correct to put in a zero instead. I did that and it was accepted. Reason is the IRS is way behind in processing both e-filed and paper returns. They are still working on returns filed in July last year. Therefore they do not yet have my 2019 AGI number in their system and this is why it was rejected. Scroll through and you will see where a Turbo Tax employeed povided a link to the IRS website explaining all of this which was very helpful to read as I was a little concerned about putting in a zero, but not any more as it's stated to do so on their website. Keep in mind too that the deadline to file as been extended to May 15.
