Comment 1 for bug 1893278

That error means it's not getting the expected relation data from Vault (or the flags driven by that data are not being set properly). I've usually seen this when deploying on AWS without a single-subnet VPC due to the ongoing issue discussed in this stuck PR: https://github.com/openstack-charmers/charm-interface-vault-kv/pull/6

There may be other causes for it, though.