Bug: Curve Animation playback differs between in editor and in game

When copy pasting keyframes in the animation editor and using the “Use Auto Tangent” feature, it will work as expected in the editor but when the animation is played in game, it is as if the tangent is never set and it interpolates jarringly.

This issue occurs in varying severity with nearly a hundred of my animations, the only workaround I found is to manually set the tangent of every joint in every keyframe by grabbing and dragging.

Minimal reproduction:

anim-bug-repro.rbxl (78.1 KB)

This place file contains one of my animations that exhibit the bug, and a script to play the animation when test played, though you will need to manually publish the animation and replace the id in the script for it to load.

In the animation editor, you will see after the main arm swing movement, the body is still but when played in game you should see a jarring bounce when it should be still.

This post is a bug report but I cannot post in the bug reports category.


can confirm this is happening
i have this bug too


I was able to repro this on studio Version 0.628.0.6280391 (64bit)
In Playtest

In Animation Editor


Update, also “Use Auto Tangent” doesn’t have to be explicitly used, curve animations seem to use auto tangents by default when creating a new keyframe, and this is enough for the bug to occur.