What causes a looping particle effect starting empty instead of prewarmed?

Prewarm is off (or the system is not looping), so the simulation begins at time zero with no particles instead of starting as if it had already been running.

How do I catch this when it only happens for some players?

Capture it automatically from the player's device with the full stack trace, the device and OS, the build, and a breadcrumb trail of what they did. That turns a vague complaint into a specific, reproducible issue you can fix without owning the hardware it happens on.

How to Fix Particle Prewarm Not Filling the Screen at Scene Start

Quick answer: Enable Looping and Prewarm in the Main module so the system spawns a full steady-state set of particles the instant it starts.

Prewarm advances the simulation by one full loop before the first frame so ambient effects look established immediately. It only works on looping systems. Here is how.

How to fix it

1. Enable Looping first

Prewarm only applies to looping systems. Turn on Looping in the Main module; a one-shot cannot be prewarmed because it has no steady state to simulate forward to.

2. Turn on Prewarm

Enable Prewarm. The system simulates one complete loop duration before frame one, so rain, fog, or dust appears already filling the area instead of building up.

3. Mind start delay

Prewarm is incompatible with a non-zero Start Delay. Set Start Delay to zero, or the engine ignores prewarm and you are back to an empty start.

Catching the ones you can't reproduce

The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.

Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.

This is where a tool like Bugnet earns its place. Its SDK captures every Unity error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.

The bug you can't reproduce isn't gone — it's just invisible until you capture it from the player's device.