OK, issue resolved.
As you recommended I added the Write Kern Table parameter to the instances tab of the font info window, since it’s a hidden parameter I pasted it in by copying this text:
> (
> {
> "Write Kern Table" = 1;
> }
> )
I also had to export the file as a True Type font, as was recommended for Office users in this thread.
For posterity:
Glyphs 2.4.1
Motion 5.3.1
362 kerned pairs