in answer to your first post, it fails on an admin account in my proper name. that was with 5.4. I also set up another admin account, and using this account, Lightroom lets me log in.
For your next post, I get the spinner on my proper name account with 5.5. I did a clean install for 5.5 as well. Logging into the other admin account, lets me login into lightroom mobile as before.