Scripted tween: weird artifacts....a bug !?

I’ve done a very simple tween of 25 lines of text, with one line fading in when the other fades out.

The original was a bit different with 3 lines being displayed at the same time, but I needed to make a different version with one line visible only.

BUT this new version is giving me weird artifacts on top of the text, like there’s some irregular kind of mask on top of each layer.
I’m really puzzled…I made it again, starting again from the original, but the same thing happened!!

I really don’t know how to fix this very strange problem of a non-existent mask/artifacts, so any kind of help is very much appreciated! :slight_smile: