There was a server crash back in February and a lot of data got lost and/or corrupted. Since your stuff hasn't come back yet, it likely never will. As sad as it is, I recommend you start rebuilding (on this account or on a new one if you're hopeful).
Check your "Bookmarks" tab and your "History" tab. Are those empty too? If not, that can be a place to start :)
Also the people in the questions section here are more than happy to help you find a manga you don't remember the name of if you describe it. Who knows, maybe someone is looking for a manga that you're missing from the lists. What I'm trying to say is, this questions section is also a great place for rebuilding your lists :)
Whyyyyyy?! What happened to my account ╥﹏╥