Try posting the material workup for the sand, and a screenshot of the area to be painted in the level. It sounds like a bug, but could be a broken node or something in the material, or a setting that doesn’t work for the square area to get painted. UE has some pretty crazy quirks that happen in materials and landscapes. I had problems with landscape painting update times, where I would paint a small area, and it would start compiling shaders in the thousands, or even in the hundreds, and took at least several minutes to complete every paint. That was some simple materials that had almost small detail level. I’m running low specs too, with an integrated Intel 5500U @ 2.4 GHz and 6 GB DDR3 RAM.