A broad, bell-shaped intensity component is observed in low-energy electron diffraction from high-quality epitaxial 2D-systems. Three 2Dsystems, graphene on Ir(111), graphene on SiC(0001), and hexagonal boron nitride on Ir(111), have been prepared in situ under ultra-high vacuum conditions. In all three systems—independent of substrate material—similar strong diffuse intensity is observed, exhibiting a width as large as 50% of the Brillouin zone and an integrated intensity more than 10 times the intensity of the Bragg spots. The presented experimental results provide evidence for a common origin of such diffuse diffraction intensity in different atomically thin 2D-materials.