Ok, you need to set in the variables the values that could affect other players. The default action is this:
Cinematic - Apply a filter over 2.00 seconds using Normal blending on texture White Mask, starting with color (100.00%, 100.00%, 100.00%) and 100.00% transparency and ending with color (0.00%, 0.00%, 0.00%) and 0.00% transparency
Now, if you apply this, the screen will become black after 2.00 seconds, because the "ending" coloring has 0% transparency, which means that it will display black coloring.
So, in order to hide the filter from the rest of the players, both starting and ending colors must have 100% transparency. So, set two variables before the Custom script action: