How to Fix an Animation Event Firing Twice After a Crossfade in Unity

Your footstep sound plays twice when transitioning between walk and run. Both clips have the footstep event and the crossfade samples both, so the handler runs twice. Removing the duplicate or guarding the call fixes it.

How to fix it

1. Keep the event on one clip

If walk and run both have the same event during a blend, remove it from one so only a single clip emits it across the crossfade.

2. Guard the handler with a cooldown

In the event handler, ignore calls that arrive within a few milliseconds of the last one using Time.unscaledTime, which collapses the duplicate from overlapping clips.

3. Move logic to a StateMachineBehaviour

For per-state actions use OnStateEnter/OnStateExit on a StateMachineBehaviour, which fires once per state transition rather than once per sampled clip.

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.