When running in FME Desktop 2016.1 using both 32-bit / 64-bit versions. I'm encountering this error while writing to the ArcGIS Portal Feature Service. The same error is found when deployed to FME Server. After being able to connect to the portal and while the writer is requesting the metadata, it encounters this error.
ArcGIS Online Feature Service Writer: Requesting metadata for layer/table 2 of Feature Service at <Portal Service URL>
Python Exception <KeyError>: 'hasZ'
A fatal error has occurred. Check the logfile above for details
This does not happen in FME Desktop 2017.