Sorry I wasnt able to get around to it until recently, but I did some tests in a new project and also wasnt able to reproduce the error. It seems to work fine even without sub-stepping.
It might be worth mentioning that my project has existed since 2014, and has just been converted since by means of copying as new engine versions have been released. If that is the reason why, is there any easy way to sort of update my project to ensure it doesnt have any kind of clash? Is it as easy as just making a new DefaultEngine.ini and re-entering my settings?