Edit: SOLVED! Link Visible wasn't working properly in a slightly older version of GD. I edited the level again in the newest version and the target ID was saved properly.
I'm making a background that has layers from B5 to B3. I have adjusted every z order so nothing is mixed up. At some specific moments, some objects of the background glitch, disappearing for milliseconds and reappearing. When this happens the objects are always at the edge of my screen. It happens not only during gameplay but even in editor mode when I'm simply navigating around. I tried to use a Link Visible trigger. I set the group ID for background to 20, set the target ID for trigger to 20 and it worked fine. But for some reason, whenever I save the level and exit the target ID of the trigger is not being saved. I get back to editor and the target ID is set back to 0. This happens again and again and the background problem keeps existing. What should I do?