I had exactly this problem. efile was rejected for incorrect AGI. But it was correct. I also verified my transcript on the IRS.gov site. It was correct.
I did see somewhere else that if your return was not confirmed in the IRS system by Nov 2020 you need to enter 0 as the AGI.
I filed a paper return early for 2019 (March 2020) but the IRS didn't process it until Feb 2021 (yes, 2021).
Anyway, entering 0 worked and my efile return was accepted. It seems odd but it looks like an IRS glitch not a TT one.
