Use the Lit shader variant stripper for terrain shaders.

com.unity.render-pipelines.high-definition/HDRP/Editor/Material/Lit/LitShaderPreprocessor.cs

             stripperFuncs.Add("HDRenderPipeline/LitTessellation", LitShaderStripper);
             stripperFuncs.Add("HDRenderPipeline/LayeredLit", LitShaderStripper);
             stripperFuncs.Add("HDRenderPipeline/LayeredLitTessellation", LitShaderStripper);
+            stripperFuncs.Add("HDRenderPipeline/TerrainLit", LitShaderStripper);
+            stripperFuncs.Add("Hidden/HDRenderPipeline/TerrainLit_Basemap", LitShaderStripper);
         }
     }
 }

com.unity.render-pipelines.high-definition/HDRP/Material/TerrainLit/TerrainLit.shader

     #pragma only_renderers d3d11 ps4 xboxone vulkan metal
 
     #pragma shader_feature _TERRAIN_8_LAYERS
-    #pragma shader_feature _ _TERRAIN_BLEND_HEIGHT
+    #pragma shader_feature _TERRAIN_BLEND_HEIGHT
     #pragma shader_feature _NORMALMAP
     #pragma shader_feature _MASKMAP
     // Sample normal in pixel shader when doing instancing

com.unity.render-pipelines.high-definition/HDRP/Material/TerrainLit/TerrainLit_Basemap_Gen.shader

         #include "../Material.hlsl"
 
         #pragma shader_feature _TERRAIN_8_LAYERS
+        #pragma shader_feature _TERRAIN_BLEND_HEIGHT
-        #pragma shader_feature _ _TERRAIN_BLEND_HEIGHT
 
         #ifdef _MASKMAP
             // Needed because unity tries to match the name of the used textures to samplers. Masks can be used without splats in Metallic pass.