Gaussian Blur not rendering on Premiere Pro

Hi there, there is something wrong happening with some of my clips on a project I'm working on.

So basically some of the clips I'm using are portrait while my sequence is landscape, so I decided to create a effect using the same clip on the background taking the whole scene, added gaussian blur and a black layer so it will make a contrast with the original which is smaller cus it's portrait.

Weird thing is that after I hit enter to render, the background will be completely black. Weird thing is that only in certain times it will happen. On the same clip it will be black and then suddenly reappears. It's the same clip, no values were changed but in one point it's black and in another point it's fine. If I raise the gaussian blur 1 up or 1 down it will appear again. Then if I render again it might be black again in certain point (I noticed it's always black in the beginning and then it appears right before the clips change).

I noticed that if I change the opacity of the black layer (even if 0.01%) it will show up again, but again If I render the thing the problem comes back. So weird. Any solutions? Looks like any changes will fix it but then when rendering it comes back.

Is that some bug or is it just my screen? I've never seen this before. Does anyone have the same issue?

Here are some screen shots from the same clip in different frames. See that on the first one it's black and then it suddenly is 'good' again.

> clip doesn't appear

> clip appears again

Edit: I changed my Renderer on project settings to Engine Software only and it seemed to fix the problem. When doing this I also noticed that actually the opacity of my blacks were way too high. What was happening is that GPU were making my blacks "not so black" so I had to push the opacity way too high to arrive where I wanted.

Now I had to change all my opacity of the black layers to a more "normal" value. I was using 98.8% of opacity and could still see the background. Why was my GPU doing this? Is there any way to fix it? I want to use my GPU but want it to behave normally.

Please if anyone know the answer let me know. My computer is also a bit slow so I'm afraid it can be a hardware issue with my graphics card.