Hi @hemub441,
This error seems to be one reported by the remote AWS API rather than by Terraform itself, and so the appearance of this error to be more likely to be caused by upgrading the AWS provider than by upgrading Terraform CLI itself.
Did you also upgrade the AWS provider during your migration? Did you use the pre-upgrade checklist for your upgrade to Terraform v0.12, and follow its advice to upgrade the provider and see the new version working with Terraform v0.11 first, before upgrading to Terraform v0.12?