HOW did you update the bios on that X470? Just pick the latest? If so, I'm betting that's the issue.
The older boards had a smaller bios chip (blame the vendor cutting costs, not amd). Consequently, the amount of info, tables, bug fixes, instructions etc needed to update a bios is more than the bios chip can contain.
So updates must be done in sequence. Hopefully you can revert back to an original bios or at least an older version pre-3rd release.
The problem lies with the changes themselves. If the original bios had XYZ, an update contains data to change XYZ to 123. A newer update contains data to change 123 to ABC. What it doesn't contain is data to change XYZ to ABC, skipping the 123 needs. Not enough room for all the possible changes.
So you'll need to update several times, the notes in the bios updates themselves will tell you which prior update is a necessity before continuing.
If you don't follow the sequence, you get a new version bios, that still contains XYZ, because there was nothing to tell it to change to ABC in the first place. The 1300x is a first release cpu, so automatically will use XYZ without issue, but the 3rd release 3900x throws an error because it can't find ABC.