It may appear to be an Xorg or lightdm/gdm/mdm error but in reality for many users with this issue, it's a driver conflict and issue. I had a system that had two GPUs, an Intel and Nvidia GPU.
The only thing that got it working was to remove the nouveau driver and blacklist it so it never came back, then the Intel GPU works fine without these issues.
Solution
sudo rmmod nouveau
add nouveau/other driver to blacklist
edit th........
This seems to happen on most if not all Nvidia cards but the good news is that if you are using any of the Linux drivers and have the nvidia-settings tool installed it is just a simple command.
Solution:
nvidia-settings --assign CurrentMetaMode="nvidia-auto-select +0+0 { ForceFullCompositionPipeline = On }"
Enter the above command in your terminal and the screentearing will be fixed which is like enabling Tear Free on AMD cards.&........
When using the .sh script the rendering doesn't work after an upgrade of related packages to kdenlive.
kdenlive (kdenlive:amd64 (4:17.04.1+git201705191233~ubuntu16.04.1)) with affine or composite transitions was fine but is now broken during the time of transition it is just a white screen.
The previous version was fine:
kdenlive:amd64 (4:17.04.1+git201705191233~ubuntu16.04.1
But now I can't find it or install it:........