If you only see a partial load, then the cause is most likely that one of the engines was found defunct or it took too long to launch and the test has started without it..
This is normal and can happen occasionally.
You can see the occurrence in the log files. Either the engine's log file will be missing (defunct) or there will be an error in the console log when trying to connect......probably both.
In case of a defunct engine, a message will appear in the test session dashboard.
In either scenario, we recommend restarting the session (press reboot). This should solve the common scenario of the engine taking too long to launch.