Hi Will,
The fact that a straightforward example works makes me thing that this may be: a) project related, b) template related.
Could this be a case of two notes in the project assigned to “AdvancedWordExport properties”? You can use the “Export validator” to check for this situation:
Did you make any recent changes to the report template around the properties? Something I know sometimes causes issues is if the default property value in Word has a typo (which causes the content to have wavy red underline).
HTH,
Daniel