Triggers that occur when the timeline of an object starts or ends may not work. If possible, apply these timeline-based triggers to the slide itself rather than individual objects.
For example, if a button is hidden and you want it to appear based on the value of a variable, add a trigger that changes the state of the button when the timeline of the slide starts (not the timeline of the button itself). You can't trigger the button to appear when the timeline of the button starts, because the timeline of the button won't start until the button appears. However, you can trigger the button to appear when the timeline of the slide starts.