Lists erased

Wait a while and refresh.

Every now and again my lists become unavailable, but they pop back up again after a while. I have never found out why but it might be the pages are being updated or they are running some process on it.

Please make sure you are logged in using the same account that was used to create the lists. When you say you 'connected your accounts', it suggests that you might have logged in via a different name.

99% of the time, when users report that their lists/votes have disappeared is because they logged in via Facebook or other credentials and have accidentally created a separate login.

Yap, that's it: old username/account still exists and lists are there. Thanks, Giancarlo!
Question remains: what is the point of connecting accounts (logging via diffrent source) if your gonna get (basicly) a new, empty, sheet?

I don't know what you did exactly so this response is necessarily a bit vague, but I suspect that when you said you 'connected' your account you simply logged in via a different authentication method.

In other words, I imagine you already had an IMDb account registered to something@something.com which you used to create your lists. Then at some point, instead of logging into your account with your username and password, you logged in via Facebook or Gmail or a different authentication method.

When you do that, you are not 'connecting' your accounts -- you are basically logging in using your other account (e.g. Facebook) as your credentials, i.e. instead of telling our system "I'm the IMDb user whose email is something@something.com and whose password is ABC123" you are telling it "I'm the IMDb user whose Facebook account is XYZ". If the Facebook account is registered to an email address that is not already present in our files, a new IMDb login is automatically created.

This will result in the creation of a different/separate account (because the login page has no way of knowing you already have one).