Media files first frame flickering black when played? And using media files in UI in general?

Hmm hmmm some progression again, but new problems as well. Now I tried creating an animated material from a big flipbook texture, that I attached on the UI image.
While it displays the animation bug-free, I cannot control the start timing of the material…thus it can start from a random frame in the middle, when I set it “visible” in the widget.
As a material, it also doesnt send any information when it has finished its loop, thus it will be looping endlessly. I can use “delay” node, but it doesnt sound like a safe way to go, especially since I am using time dillation as well.