You always need to use the amount from your original return -- the one you filed first -- not the AGI from any amended return.
Please see the TurboTax Help articles “What do I use for my AGI if I filed late, amended, or got a notice changing my return?” for more information, and “E-file reject IND-031-04 or IND-032-04: The AGI or Self-select PIN from last year doesn't match IRS ...” for guidance on how to fix and re-file your return when this error occurs.
There may be an issue with the IRS not being able to match your 2018 AGI with their records. You may want to consider filing a paper return. A paper return will not have the AGI issue you are having as the AGI is only used to verify your identity when you efile.