The \ must be before *.
My script which works:
E:\UnrealEngine\Engine\Binaries\Win64\UnrealEditor-Cmd.exe E:\MyProject\MyProject.uproject -run=ShaderPipelineCacheTools expand E:\MyProject\Build\Windows\MyProject\Saved\CollectedPSOs_Copy/*.rec.upipelinecache E:\MyProject\Build\Windows\MyProject\Saved\CollectedPSOs_Copy/*.shk E:\MyProject\Build\Windows\MyProject\Saved\CollectedPSOs_Copy\PSOCacheTest_MyProject_PCD3D_SM6.spc
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