What causes Unity foot IK that never applies?

The Animator layer running the locomotion does not have IK Pass enabled, so OnAnimatorIK is never called and your SetIKPosition calls do nothing.

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 Foot IK Not Applied Because the IK Pass Is Disabled on the Layer

Quick answer: Enable IK Pass on the relevant Animator layer, then set foot goals in OnAnimatorIK using SetIKPositionWeight and SetIKPosition each frame.

Foot IK that snaps feet to the ground requires the Animator to run an IK pass on the layer driving the legs. If your OnAnimatorIK callback never seems to fire, the layer's IK Pass is off. Here is the fix.

How to fix it

1. Enable IK Pass on the layer

In the Animator window, open the layer's settings via the gear icon and tick IK Pass. Unity only invokes OnAnimatorIK for layers with this enabled.

2. Set goal weight and position

In OnAnimatorIK call animator.SetIKPositionWeight(AvatarIKGoal.LeftFoot, 1f) then SetIKPosition with the raycast hit point. A weight of zero leaves the original animated foot untouched.

3. Raycast per foot for slopes

Cast down from each foot bone to find the ground and also rotate the foot with SetIKRotation to match the surface normal, so feet plant flat on slopes instead of clipping.

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.

The bug you can't reproduce isn't gone — it's just invisible until you capture it from the player's device.