The event driven loader is unavailable in binary engine distributions. Only source code distributions can use it. A warning message about it is logged to the output window when attempting to enable it in non source code distribution.
The Event Driven Loader checkbox is unchecked (false) by default, however attempting to click it does not set it to checked (true). Attempting to set s.EventDrivenLoaderEnabled=True in the DefaultEngine.ini file reverts to False when the project is opened.
Checkbox remains unchecked / disabled
Setting switched between false/true when the checkbox is clicked.
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