Recovery of a cross-account DR copy of encrypted RDS snapshots
There is a limitation for restoring encrypted RDS snapshots from a DR AWS account. This is an AWS limitation, as described in this link .
"Sharing an unencrypted manual DB snapshot enables authorized AWS accounts to directly restore a DB instance from the snapshot instead of taking a copy of it and restoring from that. This isn't supported for encrypted manual DB snapshots."
As a workaround, you can either restore directly to the DR AWS account, or the snapshot data can be copied back to the original AWS account, and then the restore can work as intended from there.