A warning triangle next to folders and documents means that this item contains deviating permissions and these might differ from its parent level.
In this example the document 1.8.2.6 has deviating permissions from its parent level(s). That is why the folders 1.8.2, 1.8 and 1 show a warning triangle together with the document 1.8.2.6.
If you wish to let a folder or document to inherit the permission from its parent level, simply click on the icon. It will disappear.
To make sure all permissions are set correctly, download a Permission Report in the Reports section.