Thread:Extension talk:Lockdown/Extension doesn't work with 1.16.0/reply (3)

There was a full thread on this showing how to reproduce exactly the same issue you're seeing but by deleting the PHP session on the server itself... apparently it wasn't migrated over when the discussion was switched from a one-page flat format.

I tried to work extensively to get it brought to someone's attention. Admins here seem more interested in telling users they're wrong and don't know how to use the extension rather than investigating the issue and trying to figure out where it's coming from for some people.