I made some progress (also tried many other things) but now I am puzzled by why when I load the scene I see something that is not in my timeline.
There is for example a text element that at 00:00,00 is set to opacity 0% (instant)
At 00:04,15 it is set to opacity 100% (instant)
But when I load the preview I see this element, why?
the file is here https://jeroencarelse.com/wp-content/uploads/2018/04/drag-start-screen-question.zip
Many thanks again for the support. Without the support I would have given up. Have also watched many videos but somehow I miss some essential logic, somewhere