You need to be able to move the random pattern around quickly.
One way, is using a panner node, but it’s very hard to make it look like it’s not panning 
Until I ( or any else ) finds a fancy way of making pseudo random numbers in a material, you’re stuck with writing to parameters from blueprint. Here, I’ve used a material parameter collection, because it’s much easier than fiddling around with a material instance
I wrote to it from the level BP with
How exactly you do that last step is up to you. This also works
Also, the texture matters a lot, I found this good
which is from
https://www.unrealengine.com/marketplace/en-US/product/luos-s-noise-texture-pack