One time, I was able to get this working again through some combination of:
- Settings / Safari / Clear History and Website Data;
- Settings / Safari / Advanced / Website Data / Remove;
- Restarting both apps.
But I'm not sure which really did it.
Any idea what causes it, how to make it never happen again, or at least how to get a god damned error message saying "the god damned link was not god damned saved"?
Note that this is not a problem with iCloud not syncing the reading list between multiple devices -- it's not even making it to the local Safari reading list.
(You may be itching right now to tell me about some third party cloud bookmark tool. Please don't.)