Game crashing on mobile fine in PE

HI guys ,
i need some help i have an issue where my game is crashing on launch from mobile but fine from pc the crash report has this in it can some one point me in the write direction

<ErrorMessage>Fatal error: [File:D:\Build++UE4+Release-4.17+Compile\Sync\Engine\Source\Runtime\Engine\Private\Materials\MaterialShared.cpp] [Line: 1867] Couldn’t find Shader TShadowDepthPSPixelShadowDepth_NonPerspectiveCorrectfalse for Material Resource MasterSubsurfaceColourMaterial! RenderMeshShaderMap 1, RenderThreadShaderMap 1 GameMeshShaderMap 1, GameThreadShaderMap 1, bShaderWasFoundInGameShaderMap 0 With VF=FInstancedStaticMeshVertexFactory, Platform=PCD3D_ES2 ShouldCache: Mat=1, VF=1, Shader=0 MaterialUsageDesc: LightingModel=MSM_TwoSidedFoliage, BlendMode=BLEND_Opaque, SpecialEngine=0, TwoSided=1, TSNormal=1, Masked=0, Distorted=0, WritesEveryPixel=1, ModifiesMeshPosition=1, Usage={bUsedWithStaticLighting,bUsedWithInstancedStaticMeshes}</ErrorMessage>