Are there plans to refund premium users for thIs month due to this ongoing issue? This is a big part of why I, and I'm sure many other users, pay for the premium membership not to mention this is a serious issue that has gone unsolved with no response for over a month.
I think this may be related to the setting for sync quality. I was having this issue on two iOS devices, and after switching the sync quality to another setting and back again (ie normal to extreme, then back to normal), it synced fine on both devices the next time I opened the app. Just be sure to choose "resync" when you get the alert about different sync quality.