Okay, looking at the materials that are used in this particle system, we noticed that they were set to be Default Lit, whereas our game runs with all lighting turned off, and all materials set to Unlit and emissive. All other devices we’ve tested on seem to deal with this okay, but it seems possible that this is causing the iPhone 5S to freak out. We’ve changed these to Unlit now, and are going through the process of testing it on a 5S, but it will take quite a while, as the Testflight build has to go through Apple’s testing process, which usually takes 8-12 hours.