What causes a Unity coroutine that does not run?

You called the coroutine method without StartCoroutine, the object was disabled or destroyed (stopping the coroutine), or a yield never completes — so the routine never runs or halts midway.

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 a Coroutine That Doesn't Run in Unity

Quick answer: Start it with StartCoroutine, keep the owning object active for the coroutine's lifetime, and make sure each yield condition is reachable.

A coroutine that does nothing was usually never started, or its object was disabled. A coroutine that stops midway hit a yield that never completes. Here is how to fix both.

How to fix it

1. Start it with StartCoroutine

Calling the coroutine method directly returns an IEnumerator and runs nothing. You must pass it to StartCoroutine. This is the most common reason a coroutine never executes.

2. Keep the object active

A coroutine stops when its MonoBehaviour's GameObject is disabled or destroyed. If the routine halts partway, check whether the object was deactivated. Run long-lived routines on an object that stays active.

3. Make yields reachable

A yield waiting on a condition that never becomes true (a WaitUntil that never passes) stalls the coroutine forever. Confirm each yield will complete, and add timeouts where appropriate.

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.

Ship the fix, watch the signature disappear from the next build. That's how you know it's really gone.