What causes objects falling through the floor in Unity?

It is collision tunnelling: a fast-moving Rigidbody travels far enough in one physics step that it is past the floor before the next collision check runs, so the contact is never detected.

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 Objects Falling Through the Floor in Unity

Quick answer: Switch the Rigidbody's Collision Detection to Continuous (or Continuous Dynamic), give the floor a thicker collider, and lower the Fixed Timestep so physics steps more often relative to the object's speed.

An object that rests fine but punches through the floor when it moves fast is the classic tunnelling bug. Discrete collision detection only samples positions each physics step, and a fast object can skip the floor entirely between samples. These settings fix it.

How to fix it

1. Set Continuous collision detection on fast bodies

On the moving Rigidbody, change Collision Detection from Discrete to Continuous or Continuous Dynamic. This sweeps the collider along its path between steps instead of only checking endpoints, catching the floor it would otherwise skip.

2. Make thin colliders thicker

A paper-thin floor or wall is easy to tunnel through. Give static surfaces a collider with real depth — even an invisible thicker box collider behind the visible mesh — so there is more to hit.

3. Lower the Fixed Timestep

In Project Settings, Time, reduce Fixed Timestep (for example from 0.02 to 0.01) so FixedUpdate and physics run more often. Each step covers less distance, shrinking the gap an object can jump.

4. Move Rigidbodies with physics, not transform

Setting transform.position teleports past colliders. Use Rigidbody.MovePosition or apply forces so the physics engine integrates motion and can resolve contacts along the way.

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.

Reproduce it once with full context and the fix writes itself. The hunt is the expensive part.