This is related to bug 49723. When $wgMFLogEvents and another extension is present/loaded with a dependency on ext.EventLogging, we get a JS error - for instance:
Uncaught Error: Unknown dependency: ext.eventLogging load.php:10078
(anonymous function) Main_Page:225
We force the ext.EventLogging target to desktop when $wgMFLogEvents is false, but do nothing for other modules that may load that have dependencies on it.