Hey Ben,
Does sound more like a question for google, but just looking there I see a difference in those pages:
the not-working ones don’t have a trailing slask; the working one does.
What happens if you ask google to index the trailing-slash version of the page? Does that work any better?
The other thing to keep in mind is whether your site has prerendering enabled, since that will “load your page” differently for google, than you do in a browser! But, I can see you do not have this enabled on this site. If you did, you’d connect more like described in this support guide (but again, this does not seem to be your situation today!):