What causes duplicate DontDestroyOnLoad singletons in Unity?

Each time the scene containing the singleton loads, a new instance is created and marked DontDestroyOnLoad, so returning to that scene stacks up copies that all run.

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 Duplicate DontDestroyOnLoad Singletons in Unity

Quick answer: Add an Awake guard that destroys any new instance when one already exists, and only put the singleton object in your very first scene — not in scenes you reload.

Two music players, two managers, doubled events after returning to the menu — that is the duplicate-singleton bug. DontDestroyOnLoad keeps the old one alive while the scene spawns a new one. The guard pattern stops it.

How to fix it

1. Add the instance guard in Awake

In Awake, if a static Instance already exists and is not this object, Destroy(gameObject) and return. Otherwise assign Instance to this and call DontDestroyOnLoad. This ensures only the first copy survives.

2. Keep the singleton out of reloaded scenes

Place the persistent object only in a bootstrap or first scene that loads once. If it lives in a scene you reload, a new copy is created every time even with a guard — the guard just cleans it up.

3. Unsubscribe events on the destroyed copy

Before destroying the duplicate, make sure it has not already subscribed to events or started coroutines, or you get doubled callbacks. Do the guard first thing in Awake, before any registration.

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.

Reproduce it once with full context and the fix writes itself. The hunt is the expensive part.