I also encountered the same problem. I tried to change my password after receiving word of the password strength assessment but even if I type a password longer than my old password it still came out with a message that my password is “too short”
I had the same problem with a password that was “strong” and around 14 characters long. I ended up having to get a new password from WordPress — much shorter! — to log back in. Something seems not to be working properly yet.