Web services are disabled when web server is being started. As Tomcat waits for servlets to answer, requests fail on timeout when startup is longer than Tomcat waiting time. It occurs for example on version upgrades when Elasticsearch indices are being populated.
curl -L -v --max-time 10 http://127.0.0.1:12475/api/system/status
* About to connect() to 127.0.0.1 port 12475 (#0)
* Trying 127.0.0.1...
* Connected to 127.0.0.1 (127.0.0.1) port 12475 (#0)
> GET /api/system/status HTTP/1.1
> User-Agent: curl/7.29.0
> Host: 127.0.0.1:12475
> Accept: */*
* Operation timed out after 10002 milliseconds with 0 out of -1 bytes received
* Closing connection 0
curl: (28) Operation timed out after 10002 milliseconds with 0 out of -1 bytes received