Using this I get the error:
*** -------------------------------------------------------------------------
*** Error: Unable to open MeshFunction for reading.
*** Reason: Mesh Grid with data Attribute not found in XDMF.
*** Where: This error was encountered inside XDMFFile.cpp.
*** Process: 0
***
*** DOLFIN version: 2019.1.0
*** Git changeset:
*** -------------------------------------------------------------------------
The same error message popped up in Fluent.msh to XDMF; error was it ever resolved?