A manual sync button and a sync processing bar or last successful sync time notice in Sync window.
Currently, I met a sync problem, and many others are same too: https://forums.opera.com/post/74097
Here I don't want to complaint the fault of the sync, but a UI lack I think we need related by sync functions.
If the sync is OK, I wouldn't find this will be a problem, but if there is some issue on sync, I believe users need a status of the sync, like: what's the last successfully sync time? How many bites been synced last time, etc.
And a manual sync button always helpful for user to make sure the sync is occur.
These functions should be added in both desktop version and mobile version.
+1. If you think the features are too "advanced" for "normal users", you can make this optional or something, just so we that want to see this can see it.