Shared reminders not working

I've been using several shared reminder lists with a family member for groceries at different stores etc and after months of working perfectly, it just stopped syncing in one particular direction (their updates to my shared list never make it to me).

I've had all sorts of iCloud syncing issues (devices within the same iCloud account, and also shared things like this reminders issue) in the past and these are a nightmare to troubleshoot because Apple doesn't give any feedback or errors when things aren't working. It's very frustrating and just seems to go against the whole "it just works" motto that Apple seems to always be suggesting.

Edit: it's also very frustrating when the only suggested fixes are wipe your device and restore, or delete all your reminders (or whatever) and start over.