Have you tried force quitting the Reminders app and reopening it? Do you have any other apple devices that you are syncing Reminders with (iCloud)? Do they work? Is Reminders enables in iCloud settings?
Woks fine for me. If I go shopping on my own I don't take my phone and check off the shopping on a shared reminders list on a cellular series 4. Anything my wife has forgotten she adds to the list on her phone and I pretty much see it straight away, in fact she says she can see where I am in the shop by which items have been checked off.
When I get syncing problems, the first thing I do is to log out of iCloud and back in again on all devices. Also check that you've removed any devices you no longer have from your iCloud account, I have found these to occasionally be "blocking" syncing.
Thanks. For some reason it started working again.
You DO realize that there are tiny little deamons that live in all electronic things, and occasionally, for their entertainment, they will pull stunts such as this. If one leans down really close to the electronic device, and if one is lucky, one can hear the little deamons laughing.
This happened to me and I couldn't get Reminders to sync to the watch until I unpaired and re-paired the watch. Now I wish I could share a shopping list with my wife on Reminders. I try and it just forces her app to crash. Used to work perfectly.
This kind of snafu causes my wife and I to complain that we wish Apple would stop trying to have great streaming TV channelt etc. and actually fix the stuff that doesn't work in their existing products.