I have been using Opera Sync for years (it was called Link). The problem is that Sync has never really worked properly regarding active tabs and history (at least on mobile, never tried syncing on PC browser in the last years). For example, I actually have almost 100 tabs opened in Opera for Android, and most of them have been opened for weeks, but if I go to the Sync website it only shows a few tabs. It's not a matter of waiting a few minutes, hours or days. They are never synced properly. It only lists the last opened ones. In this moment it list also 3 URLs that aren't among the opened tabs and haven't been visited for months, I suppose they are from old History.
History too is almost useless, I can visit many web sites but it only list one or two per day, but usually it completely skips the whole day. I use Mobile Opera every day as the main mobile browser, so that's a real problem.
Is it going to be like this forever?