How to fix the outline of mask is visible on animation?

[Scale5FF5]

How to fix this white mask outlines?

[Szalam]

Without knowing a heck of a lot more information, it's going to be impossible to figure out.

What's in your comp? How did you make them show up in the first place? Since you don't know those things (or you wouldn't be asking), can you share a project file demonstrating the issue?

[Scale5FF5]

Here is an attachment

[Szalam]

Go to layers "Shape Layer 1" and "Shape Layer 2" and turn off their stroke.