What causes a Unity build that works locally but fails on CI?

CI runs a clean checkout without your local Library cache, activated license, or installed platform module, so it reimports from scratch and fails on anything your machine had cached or pre-installed.

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 Unity Build That Works Locally but Fails on CI

Quick answer: Activate the Unity license on the runner, install the matching editor version and target module, cache the Library folder, and build in batchmode with logs.

A build that runs fine on your laptop fails in CI with import, license, or missing-module errors because the runner starts clean. Reproducing your environment on the runner fixes it.

How to fix it

1. Match the editor version and modules

Install the exact Unity version from ProjectVersion.txt plus the target platform module (Android, WebGL, etc.) on the runner. A missing module makes the build target unavailable.

2. Activate a license in batchmode

Provide a valid Unity license/serial to the runner and run with -batchmode -nographics -quit -logFile -. An unactivated editor on CI fails before it builds anything.

3. Cache or rebuild the Library

Cache the Library folder between runs (keyed on packages and project version) so reimport is fast and deterministic; on a cold cache, allow extra time and read the full log for the first real error.

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 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 errors you never hear about are the ones quietly costing you players. Visibility turns them into a worklist.