Composite Mode not working

Hello,

I encounter a technical probelm on my DaVinci Resolve 15.0 in EDITING mode.

I'm using layout clips with a flare effect in order to merge them with my footage on the timeline.
For that, I go to the Inspector > Composite Mode > I select "Screen" for the layout clip, which is on top of my footage.

It worked for a while and I did some exports of the video with OK result. But then the blending effect stopped working with some random clips. Now, whatever I do with these clips, the composite mode Screen doesn't make it to the exported video. It only exports the clip "on top" of the timeline, which is the layout clip with a black background, masking the video.

Do you have any idea what the reason of this problem is and how to solve it?

For you information, I have regularly "GPU Memory Full" messages", but that never stopped me from doing anything. Could that be related to my current problem? I'm on MAC OS 10.13.5.

Thank you in advance for your help!

(*Sorry for my English if I left some mistakes)

That could be related, Resolve relies heavily on the GPU.
Which GPU and how much VRAM do you have?
Which resolution in the timeline?

That could be related, Resolve relies heavily on the GPU.
Which GPU and how much VRAM do you have?
Which resolution in the timeline?

I have a MAC OS 10.13.5 with 8 Go VRAM 1600 MHz DDR3
Graphism: Intel HD Graphics 4000 1536 Mo
I am running with the NVIDIA Web Driver 387.10.10.10.35.106

The resolution in the timeline is 1080p 50fps (with the layout clips originally in 4K)

What's your other GPU? The Intel Graphics has no 8 GB VRAM and doesn't need the Nvidia driver.

Or did you misunderstand my question? Do you actually have only 8 GB CPU RAM, not video RAM (VRAM)? If so, your machine is not powerful enough for version 15. Try 12.5, it's still available.