Hello, been struggling with this for a while, and may have found a solution.
In the details panel, make sure PIEHandling is UNCHECKED.
I had the video working in the media player, the material, and when loaded it would display in the viewport, but when actually doing a test play it would cut out.
Having it checked made the video unload from the playlist each time I went to playtest.
That check box effected me even with the Open Source Node connected to the Begin Play Pins.
Hope this helps anyone who might’ve ran through each step with no avail!