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Niagara system not working until I open it and it compiles - still won't work in packaged game

Hello everyone,

I’m Julien and this is my first post here!
Hope I’m in the right place for the issue I’m facing.

I’ve started learning UE4 in 2020 and I did overcome many difficulties thanks to wonderful resources available online, in this forum and other places.
Though, now is the time for me to reach out for help.

I’m working on an effect where particles are emitted from a video texture. Particles spawn on a rectangle surface, inherit from the color of the video texture corresponding to their position, and then travel at constant speed away from the rectangle.

My problem is that the effect doesn’t work until I open the Niagara System. It doesn’t seem to compile until then.
All works fine after I open the Niagara System, it works when playing in preview mode, but it doesn’t work again in the packaged game.
I am certain that it comes from the “sample texture” node in the Niagara emitter, because if I duplicate the system and delete the node, the particles are emitted (the white particles in attached pictures).
It seems that the Niagara system has trouble sampling the video texture.

Any idea on how to fix this issue?
I guess I should somehow force the Niagara system to compile via blueprint, but I don’t know enough about the engine to do so.

I hope my explanations are clear enough, tell me if it isn’t.

Thanks very much,
Happy end of the year.

Engine version: 4.25.4
Also, the video is stored in Content/Movies, as I’ve red it should be.