Creating a material with "Absolute World Position" node plugged into the "World Position Offset" input of the base Material node results in flickering in the preview window of the material editor.
The material flickers in the viewport if you have Cylinder, Sphere, or Cube selected as the preview mesh, but NOT when plane primitive is selected.
The material flickers in the viewport if Absolute World Position (Including Material Shader Offsets) or Absolute World Position (Excluding Material Offsets) node is used, but not if Camera Relative World Position is used.
This issue has been observed in 4.15-4.19.
Head over to the existing Questions & Answers thread and let us know what's up.