I have had the same problem - I can't get past the login screen on an AP903 acting as a mesh node on a 2927Lac acting as mesh root. But in my case, I find I can log in fine on firefox, but not chrome. So I am sure it's not related to the password that appears on the mesh setup page on the router, I imagine it's a cache issue or a browser extension interfering. I've not diagnosed it yet, mainly because I can access it via Firefox, so it's not an immediate problem!

Hope this helps anyone in the same position.