Hi,
Can you try the following:
Set this option :
"RenderDeferred" to 0 in the ..\Documents\Larian Studios\Original Sin\graphicSettings.lsx
To do this, find
<attribute id="MapKey" value="RenderDeferred" type="22" />
<attribute id="Type" value="0" type="5" />
<attribute id="Value" value="1" type="4" />
and change it to
<attribute id="MapKey" value="RenderDeferred" type="22" />
<attribute id="Type" value="0" type="5" />
<attribute id="Value" value="0" type="4" />
Then save the file. The only thing that changed is the 1 to 0 on the bottom line.
Then try the game again and see if it changes anything.