Particle Collision On iOS Mobile Devices
When using the Particle Collision module with VFX's that are for iOS mobile devices you will need to adjust the Min Desired Frame Rate to something lower than 30 FPS or your particle collisions will have a high probability of not colliding with objects in the world.
This is because when the frame rate of any Unreal Engine 4(UE4) project drops below 30 FPS UE4 will disable particle collisions in an attempt to keep the frame rate above 30 FPS.
By default iOS projects are locked to 30FPS which means that by design particle collisions will be disabled from the start.
To ensure that this does not happen to your UE4 iOS project you need to first go to Project Settings > General Settings > Framerate.
Once the Framerate section is opened, set the Min Desired Frame Rate to something under 30 FPS like 25 FPS for example.
Then under the Performacne section in your particel effect Collision module, uncheck the Drop Detail option.
After the Min Desired Frame Rate has been changed and the Drop Detail box unchecked,
re-cook or re-deploy your project to your iOS mobiel device and check to see if the particle collisions are working.