Failed to get from node cache

Following errors are logged in Kong

Getting error failed to get from node cache: [cassandra error] all hosts tried for query failed. 1.2.3.4: host still considered down, context: ssl_certificate_by_lua, client: 1.2.3.5, server: 0.0.0.0:443.
SSL_do_handshake() failed (SSL: error:1408A179:SSL routines:Ssl3_get_client_hello:cert cb error) while SSL handshaking

*load_plugin_configuration(): failed to get from node cache: callback threw an error: [cassandra error] [Unavailable exception] Cannot achieve consistency level ALL

This error is frequent. Can some body explain what is the root cause of this error and how to avoid this error.
Using Kong CE 0.13