In my case (paper joint return filed in March of 2020 and received - check for payment sent with return was cashed and is reported by IRS - but return still not processed) submitting 0 for 2019 AGI was again rejected, but after I entered 0 for spouse's AGI and resubmitted, was accepted. So, if filing a joint return and 2019 return still not processed, to have success filing electronically you can try entering 0 for both spouses' AGI. Worked for me, YMMV.
