What causes Unity smart merge not running on scene conflicts in Git?

Git never invoked UnityYAMLMerge because the merge driver was not registered in your git config and .gitattributes, so it did a line-based merge that mangled the YAML.

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 Unity Smart Merge Not Running on Scene Conflicts in Git

Quick answer: Register the unityyamlmerge driver in your global git config and map *.unity, *.prefab, and *.asset to it in .gitattributes so Git delegates structural merges to Unity's tool.

Scene merges produce a tangle of YAML conflict markers and broken object references. Unity ships UnityYAMLMerge for exactly this, but Git is not calling it because the driver was never configured.

How to fix it

1. Define the merge driver

Add a [merge "unityyamlmerge"] section to your git config pointing at the UnityYAMLMerge binary under your editor's Tools folder, with the correct merge command line.

2. Map the file types

In .gitattributes add *.unity merge=unityyamlmerge plus the same for *.prefab and *.asset so Git routes those files through the structural merger.

3. Force text serialization

Set Edit > Project Settings > Editor > Asset Serialization to Force Text. Binary or mixed scenes cannot be smart-merged at all, so this is a prerequisite.

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.

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