Unfortunately Premiere has never been optimal when it comes to the exported Files Metadata.
Sure might be that it worked before in ffastrans and maybe works later but that does not change the fact that AME exports a file with different Metadata in Stream vs. Container. in your specific case.
We recently discovered the exact same problem for XAVC export at work, e.g. XAVC-L was tagged correctly but XAVC-I had the exact same problem as your file did. Sure we opened a case with Adobe so they can resolve the issue in future versions. Also as we have strict file quality restrictions, we cannot use the AME feature that produces wrongly tagged files (XAVC-I export in this case) and must wait for an updated version that fixes the issue.