How to Fix “Duplicate class found in modules” Gradle Errors in Android Game Builds

Gradle refuses to build when one class exists in two artifacts. The error lists the class and both sources — the fix is dependency surgery. Here is the procedure.

How to fix it

1. Read both artifact names

The error names the class and the two modules carrying it — that pair defines the fix: same library twice (dedupe), or two SDKs bundling the same utility (exclude from one).

2. Exclude at the dependency

In Gradle: implementation(sdk) { exclude group: "com.example", module: "common" } — prefer excluding from the SDK that bundles a copy rather than the canonical source.

3. Kill jar-plus-Maven duplication

Engines' plugin folders accumulate loose .jar/.aar files that later also arrive via Gradle dependencies — remove the loose copies and depend once, via Gradle.

4. Align the ecosystem

Support-library vs AndroidX collisions mean incomplete migration — enable AndroidX + Jetifier (or update the old SDK) rather than excluding your way around it.

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 mobile 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.