I meant to send this reply to the list as well:

Hi Ken,

I originally wrote the ox-synctex code.  I find that the code in your
example works for me only after re-evaluating the two functions that
ox-synctex advises (org-export-as and org-latex-compile).  This must be
some oddity of how advice interacts with org’s code (probably having
something to do with byte compilation/autoloading).  But I’ve never been
able to isolate a simple test case.

I don’t use ox-synctex on a daily basis myself: it’s too fiddly, as
you’ve seen.

--
Aaron Ecay