You are using multiple timelines, and the build-ins are on the non-Main Timeline (for scissors for example, the build-in is on a timeline called "Cyan"). By default, only the Main Timeline is started when a scene is shown; you must explicitly start other timelines.
The simplest fix is to add an "On Scene Load" action in the Scene Inspector to Start the timeline with the build-ins. However, based on your content it is likely organizationally/logically more correct for these animations to be moved onto the main timeline via cut/paste.
Please see our overview video or documentation for more info on timelines.