If a master timeline is playing another timeline using a control track, master timeline's override animation tracks will be ignored. I've attached a project with a simple setup: there is a cube, a timeline with a clip of its vertical movement and a master timeline that plays the other timeline and overlays horizontal movement on top. To reproduce the steps in the attached project: - Open SampleScene - Open Timeline Window - Enter Play Mode by pressing play - Select Master Timeline gameobject in hierarchy - In Timeline Window, expand top Animation Track to see the override curve clip. - In Timeline Window, press play Expected: The cube moves up and down until the timeline time marker reaches the "Horizontal" animation clip, at which point it should start moving front and back. Actual: The cube just moves up and down and ignores the Horizontal animation clip entirely. If you want to see what the 2 combines animations look like, disable all tracks except the last 2 in Master Timeline and press play in Timeline Window.