Thanks! That just might be it. I have UTF-8 in the GPX file:
<?xml version="1.0" encoding="UTF-8"?>
<gpx xmlns="http://www.topografix.com/GPX/1/1" Version="1.1"
Creator="Europe Diary">
So perhaps iOS use UTF-8 and MacOS UTF-16
NO! I tried changing the XML specification to UTF-16 but no go. I will have another look at the Base elements plugin. It looks like another "Case iOS, xxx, MacOS,xxx,Windows,xxx" thing. Sigh...