Blur effect in precomp do not work in main comp when masking

Hello community,

I run into awful problem. I have some effects (like gaussian blur) on my animation, which is in pre-comp. The 3D-animation did not work in main-comp, so I skipped it. But its got text animation on it which I cannot skip. I need to reveal the pre-comp-animation in main-comp, by using masking. The problem is, the pre-comps FXs (like the blur) do not work in main-comp when I create a mask. The FXs disappear. And they reappear when I delete the mask. I need to do the masking in main-comp. I´ve tried shape layer masking and layer masking (and inverting), and it doesn´t matter if the layer mask is on "add" or "subtract". Nothing seems to get me around this problem.

There has been plenty of trouble already and this is my "plan C", or "plan D" already. I´m running out of plans. For some reason the link between main-comp and pre-comp does not work propely. Please, does anyone know, why effects won´t work with mask and is there any alternative solution?? Thank you.