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)
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)