If a request is not being processed in a timely manner, it will mark the service unhealthy, which can lead to STONITH. However, in some cases when the server is very heavily loaded, requests may take longer than at_max to be processed and this shouldn't cause the server to be killed, since that will slow down request processing even further and put extra load on the backup server(s), slowing down their processing and possibly causing them to fail in a similar manner.