I'm have been using Ubuntu 18.04 for about a year on my Thinkpad T460s.
Everything is ok until a week ago, when I turned my laptop into sleep mode (hold Windows key and click to top-right corner, click power button), I could see my laptop go into sleep mode (can be confirmed by monitor and red led on Thinkpad cover). But some hours later, I opened my laptop but it brought me straight to desktop without login screen & password! The next time suspend and wake up, it did show login screen, but the third time problem was repeated and so on, it occured alternately.
My laptop connects to an external screen and I only work on that external screen, so the lid is always closed. Everytime wake up the laptop, I have open the lid.
What can cause this problem and how to fix this?
Update: Now the above problem gone away but my laptop wake up from suspend without showing the login screen.