I'm trying to update an AGOL layer directly from FME instead of overwriting it from a file geodatabase in ArcGIS Pro to automate my workflow.

I am getting there following error as soon as the first item reaches the writer:

"Reproject: Could not reproject the geometry of the preceding feature: Reprojector: Invalid reprojection parameters

%0 Writer: Failed to reproject feature with coordinate system '%1' to '%2'. Verify that the coordinates and coordinate systems are valid, and try again

A fatal error has occurred. Check the logfile above for details"

I am using an ARCGISONLINEFEATURES writer, trying to write information that is already in British National Grid (BNG), to a hosted feature layer in AGOL that I own and is editable and is also to BNG. I have the source and destination coordinate systems set to BNG, so a reprojection shouldn't be required, but the error message above is suggesting I need to do this.

I can get the data to update/publish fine if I set the source to be BNG, and the writer to be WGS 1984, but I need the writer to be to BNG as the data is not reprojected correctly in WGS 1984 (a few metres out whereas I need millimetre accuracy). I have tried all the supplied reprojector transformers with various settings but can't get this to work.

I've tried it using two different sets of data, points and polygons, both give the same error.

Has anyone encountered this problem before?

Can the writer support publishing to British National Grid instead of WGS 1984?

Is it a bug?