Just had the same experience using the AGI from an accepted amended return for 2019. I resubmitted the 2020 return using the 2019 AGI from the return prior to the amended and this time it was accepted. My amended return was accepted 5 days ago so looks like the latency in updating the IRS database is at least 5 days. Either that or possibly the IRS always uses the AGI from the first accepted submission for any given year.
