Error updating native instances

[marktucker]

Description of Issue

There is a bug in the hydra native instancing update procedure such that the update fails given the right morphing of the stage.

Steps to Reproduce

1. Load first.usda from the attached zip file into usdview:
   instanced_cubes.zip

2. In the interpreter window, run:
   l = Sdf.Layer.FindOrOpen("second.usda")
   usdviewApi.stage.GetRootLayer().TransferContent(l)

3. An error is printed to the console:
   ERROR: Usdview encountered an error while rendering.
   Error in 'pxrInternal_v0_20__pxrReserved__::UsdImagingDelegate::_GetUsdP
   rim' at line 531 in file F:/dev_tools/src/usd/usd-20.05/USD-py2.7/pxr/usdImaging
   /usdImaging/delegate.h : 'Failed verification: ' p ' -- No prim found for id: /F
   lattened_Master_1/instancer1'
   And the viewport doesn't show the new geometry. You can see that second.usda should look just like first.usda by loading it directly into usdview.

System Information (OS, Hardware)

Tested on Windows 10.

Package Versions

Tested with 19.11 and 20.05 with the same results.

[jilliene]

Filed as internal issue #USD-5997