It would be nice if more people knew about this simple trick.
There’s a possibility that the encrypted key exists on an older config db. TrueNAS usually creates daily backups of this on your System Dataset. You can look under /var/db/system/configs-XXXX/
There’s a possibility that renaming a dataset (which bypasses the middleware) might have the same effect as exporting a pool. The dataset doesn’t “exist” anymore, so it’s possible that the key for the “disappeared” dataset was removed from the config db.