In my PRTG cluster setup, the Primary Master server failed, so one of the failover nodes took over the master role. It is the Failover Master now.
What does the crawl box mean? It is shown when I log into the failover master's web interface and says:
Cluster is in Failover Mode. This failover node is your current master node because your primary node is not connected to this cluster. You can modify the monitoring configuration, but as soon as the primary node reconnects to the cluster all your changes will be overwritten by the configuration of the primary node.