Content browser thumbnails render black


we are having an issue with thumbnails in the content browser. Every time we double click a thumbnail of a 3D asset or a material the thumbnail turns black. The same happens if we enable thumnail editing mode an single click a thumbnail.

We are using a modified version of 4.11.2

Update: The preview window of the material editor also becomes black when its width is below about 700 px. The preview appears again when the window is resized to a larger width.

This happens for us after installing TrueSky. Do you use TrueSky?

I use truesky and im having the same issues. Random items in content browser are black and will sometimes flicker visible. Very annoying. Also happening in the Landscape menu for materials there.