Media Texture not working

I have some Media Textures playing videos in an UMG.
It is working as intended in PIE, Standalone and packaged game, but only
on the machine which the project is located on. Everyone else gets blackscreens.

Only thing I found about it would be, that the source location path is absolute
but I checked and its ./Movies/xxx.mp4

Using 4.19 build from source.

So I got no idea why it’s behaving that way?
Hope somebody can help

Best regards and thanks in advance!