What causes a Bezier handle discontinuity at spline joints in Unity?

When the outgoing handle of one segment and the incoming handle of the next are not collinear and equal length, the tangent direction changes abruptly at the joint, producing a visible kink.

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 Bezier Handle Discontinuity at Spline Joints in Unity

Quick answer: Mirror the handles across the shared anchor so they are collinear and equal in length, giving C1 continuity and a smooth tangent across the joint.

A camera rail or motion path that jerks at the points where spline segments connect has discontinuous tangents. Mirroring the Bezier handles smooths the joints. Here is how to fix it.

How to fix it

1. Mirror the handles

At each shared anchor, set the next segment's incoming handle to the reflection of the previous segment's outgoing handle: inHandle = anchor - (outHandle - anchor). This gives equal, opposite tangents.

2. Match handle lengths for C1

Equal-length mirrored handles give C1 (continuous first derivative) continuity. If only directions match but lengths differ you get G1, which looks smooth but has a speed discontinuity.

3. Use a spline asset for editing

Prefer Unity's Splines package, which enforces handle continuity modes (Mirrored, Continuous, Broken) so you do not have to maintain the reflection math by hand.

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 errors you never hear about are the ones quietly costing you players. Visibility turns them into a worklist.