Nested abc/usd standin within usd standin does not apply transform in viewport correctly

[jrosenA9TLN]

Maya 2020.4
MtoA 4.2.3
Arnold Core 6.2.1.1

I'm trying to setup a nested standin/reference workflow using abc and usd (alembic doesn't support exporting/expanding arnold standins). But I've noticed when I export my geometry as .abc the geometry doesn't have the transforms applied.

+ standin --> (cube_group.usda) + group
                                  + standin --> cube.abc

Repro:

• Select and export cube at origin: Arnold --> Scene Export -> Export Selection to Alembic... (Use defaults)
• Create Standin
• Set Path to exported .abc file
• Group and set transform to 1, 1, 1
  
• Select and export group1: Arnold --> Scene Export -> Export Selection to Usd...
• Under Export section uncheck everything except Shapes and Shaders (Unchecking Full Paths didn't seem to have an affect)
• Create Standin
• Set path to exported .usd, cube appears at the origin
  

  def ArnoldAlembic "pCube1StandinShape"
  {
      string arnold:filename = ".../maya/arnold_forum/abc_cube_viewport/cube.abc"
      string arnold:name = "pCube1StandinShape"
      float arnold:radius_default = 0.01
      float3[] extent = [(-0.5, -0.5, -0.5), (0.5, 0.5, 0.5)]
      string primvars:dcc_name = "pCube1StandinShape" (
          elementSize = 1
          interpolation = "constant"
      )
      string primvars:maya_full_name = "|group1|pCube1Standin|pCube1StandinShape" (
          elementSize = 1
          interpolation = "constant"
      )
      matrix4d xformOp:transform.timeSamples = {
          0: ( (1, 0, 0, 0), (0, 1, 0, 0), (0, 0, 1, 0), (1, 1, 1, 1) ),
      }
      uniform token[] xformOpOrder = ["xformOp:transform"]
  }

• But renders correctly
  
• Repeat the above steps to export the cube as a .usda, create a standin, group and export as .usda
• The geometry is now double transformed
  

  def Xform "group2"
  {
      def Xform "pCube1_usd"
      {
          def ArnoldUsd "pCube1_usdShape"
          {
              string arnold:filename = ".../maya/arnold_forum/abc_cube_viewport/cube.usda"
              float3[] extent = [(-0.5, -0.5, -0.5), (0.5, 0.5, 0.5)]
              string primvars:dcc_name = "pCube1_usdShape" (
                  elementSize = 1
                  interpolation = "constant"
              )
              matrix4d xformOp:transform.timeSamples = {
                  0: ( (1, 0, 0, 0), (0, 1, 0, 0), (0, 0, 1, 0), (1, 1, 1, 1) ),
              }
              uniform token[] xformOpOrder = ["xformOp:transform"]
          }
      }
  }

• But renders correctly (minus shading - diff issue)
  

I thought this was fixed with MtoA 4.2.2 - Nested procedurals ignore matrix in viewport API #508, but it looks like there's still issues.

I can add zip of my file if that's useful. But I couldn't get relative paths with Arnold Scene Export to work.

[Stephen.Blair]

I can repro, thanks for reporting.

I'll post the ticket number after I log it...

Update: This is logged as MTOA-729