What causes the IsMatrixValid assertion in Unity?

A transform, camera, or renderer received a matrix containing NaN or infinity — usually a position or scale computed from a division by zero, a normalized zero vector, or physics feeding NaN velocities into a transform.

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 “Assertion failed on expression: 'IsMatrixValid(matrix)'” in Unity

Quick answer: Find the code writing NaN into a transform (log and clamp), guard divisions and normalizations against zero, and reset any rigidbody that has picked up NaN velocity.

This console spam means something set a transform to NaN, and every camera render trips the assertion. The message does not name the object, so the job is finding who wrote the NaN. Here is how.

How to fix it

1. Detect the NaN at the source

Add a development-build check where you set positions: if (float.IsNaN(pos.x)) Debug.LogError(name, this); — or a periodic sweep over transforms — to identify the object and callsite.

2. Guard the classic producers

Normalizing a zero vector, Quaternion.LookRotation(Vector3.zero), dividing by a delta that can be zero, and lerping with NaN t are the usual sources — clamp or early-out each.

3. Reset poisoned physics

Once NaN enters a rigidbody it spreads; on detection, zero the velocity and teleport the body to a known-good position rather than letting the assertion spam continue.

4. Keep the guard in release telemetry

Ship a lightweight NaN check that reports the object path and last writer, so player-only occurrences (uncapped framerate, alt-tab deltas) arrive as actionable reports.

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.

Most of the time the fix is small. Seeing the failure clearly is the part that actually costs you.