"The export failed due to an unexpected error"

Hi - running Office 365 for Business (16.0.9226.2114) on Windows 10. I can create very simple PDFs from Word using Save As>pdf (e.g. a just a document containint the text "Test"); however I'm having problems with more complex documents e.g. a template which i commonly use. When I Save As>pdf, I get a dialog box, "The export failed due to an unexpected error", and Word crashes.

So far I've tried the following:

- 3 hours on the phone to Microsoft tech support; uninstalled and reinstalled Office 365; also experimented with workaround using Microsoft XPS Document Writer, which produced an inaccurate pdf, e.g. with white strips at the top and bottom of each page. Their suggested solution was to use an alternative program, Cute pfd, which also produces an inaccurate copy.

- Experimenting with Word documents which I've previously used to successfully create PDFs using the Save As>pdf method; they also now produce the same error message i.e. "The export failed due to an unexpected error".

- Checking with colleagues who use the same template; while they experienced a similar issue a couple of months ago, they are now able to use the same template to create PDFs without any issues.

What's the solution?

Thanks