Enabled (!) Visibility Modifier do not work

Edited because: Problem solved. New Visibility Modifier are blocked by older when covering the same area. Close plz.

During a cinematic intro for my map I use some Visibility Modifiers, always created with "Create an initially Enabled visibility modifier for Player 1 (Red) across <Region>".
Vis Mods are always put into a variable after creation to be able to destroy them later.

Problem is, that after the intro no more visibility modifier seem to work. The respective triggers do work for sure but no more vis mods are created.

Are there any circumstances that prevent the use of Vis Mods ?
Like Letterbox Mode, total number of modifier (not many, btw) or anything else ?

Thx
Gozai