This issue has been closed as 'Won't Fix' due to an extended period of time without updates. If this issue is important to you please let us know by posting on the AnswerHub or UDN, and Epic will re-open the ticket for further review.
Emitter modules that are set to the "High" detail mode are removed when changing the engine scalability settings to "low", but not replaced when setting them back to "Epic." The emitter is updated correctly in cascade, but not in world. Building or simulating the level updates the emitter to its correct settings.
Observe that the flames do not spawn when reverting the detail mode back to it's maximum.
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