After updating Windows (to 1803) and the driver (to 398.11) the generation of mipmaps (DirectX 12) on Titan V stopped working. The shader takes incredible time (40-50 milliseconds for 4096x1024), but the mipmap levels remain empty. Before the update, Titan V worked without any problems. Other video cards (tested: Titan X Pascal, Titan Black Kepler and AMD R9 Nano) using the same program and shader work fine. It seems so the bug affected only the Volta GPU.
I do not know exactly where the bug is, it can be both Windows and the driver.