Overview
The error "[12057] - Revocation cannot be checked because the revocation server was offline" is caused when the revocation server is offline or unreachable to verify the SSL certificate when visiting a secure website. This error can occur when Last Mile, Backbone, and Enterprise Nodes are unable to connect to the revocation server.
Explanation
The test which triggers alerts for this error may still show as passing on the performance chart (blue dot). The test is still considered passing because the test's URL is still reachable and may be returning a 20X response code. To prevent a test from alerting for the revocation error, enable "Ignore SSL Failures" in its Advanced Settings.
See also
To learn more about different node types, refer to this article, Nodes Overview.
For more information about "Ignore SSL Failures", read this article: Advanced Settings.