Like most security conscious people I regularly change my Chromebook's password. After all, it's a jungle out there. Twice it claimed it couldn't verify my password. The third time it accepted it. Positively strange, if not a little disconcerting.
Just a thought. Could be an intermittent, dying or worn key. I had similar recently with a mini keyboard. I didn't notice it until I came to use that particular key. Sometimes when one goes a number of others can go too on the same circuit.