Hi, GreenSock Team!   Please, have a look on the Pen. On each document click it will launch the timeline, which fires the onStart callback twice(!). The bug is new for 3.7.0, because I cannot reproduce it on the older 3.6.0.   Thanks, Iurii See the Pen VwbYrNz by StGewehr (@StGewehr) on CodePen.