I have the same problem in UE 5.5.
My heightmap image resolution is 8192x8192, and I tried both 8-bit and 16-bit grayscale.
If I import the heightmap into an external tool like TerreSculptor 2.0 it looks fine, no layered bumps like in your image, but when I import the file using Landscape mode, I get the same type of bumps no matter the settings.