As you can easily see when you visit LessWrong.com, the site transfer is complete, and we are now on the new URL. The data import will run for the next few hours, and by tomorrow morning everything should be complete.
Let us know if you run into any problems, find any broken links, or anything of that sort!
Could it be browser-dependent? (I'm on up-to-date FF52esr right now.)
Edit: Also, I have now verified that the error object “LW1 user detected, legacy salt attached” appears twice in the JS console (even for a single login submission), with different JS source references (although the data in the error object itself seem to be identical). So it may be that a LW1-style login is being attempted but is failing, either because some password data got corrupted on the LW2 side, or due to some client-side issue.