In RHEL 7.3 the plone_backup_path generates a issue {"failed": true, "msg": "template error while templating string: unexpected '/'} when the playbook runs to deploy only a ZeoServer task. To fix this I just complete the sentence with "is defined" in "when" condition sentences.
Since plone_backup_path is defined in defaults/main.yml, I don't see the code path that would result in it being undefined. Please refile this as an issue with an example from a playbook.
In RHEL 7.3 the plone_backup_path generates a issue {"failed": true, "msg": "template error while templating string: unexpected '/'} when the playbook runs to deploy only a ZeoServer task. To fix this I just complete the sentence with "is defined" in "when" condition sentences.