Thank you very much for the reply Mark.
At the moment I’m just creating ALL the effect in Motion 5. Then I’m just using the Share -> Export Movie to see the result and that’s what I get. I’m using Apple Pro Res 4444 with a tick in “Premultiply Alpha”. I’ve already tried to uncheck it and the result is even worse.
I’ve also thought that it could be a composition problem. However, when I add the black background to the scene, the problem gets resolved. That led me to think that the result Motion was showing me was not real. I’m beginning to think that what I see when I export transparent is the real result and when I see it inside Motion with a black background, he’s making some kind of multiply and showing me those white stripes way more intense.
Don’t know what to do next…