SUMMARY
After waking from suspend I enter my password on a screenlocker and hit enter.
I do not touch mouse or tab key usually - only alphanums and Enter.
Usually I get to the desktop afterwards, but sometimes nothing happens. 
I am able to enter password, I see circles or letters inside input field but to login I must click on arrow-button using mouse. ENTER key does not work.
During this failure I am also unable to move cursor inside the password input field using arrow keys of my keyboard.

STEPS TO REPRODUCE
The way to reproduce (to provoke) this problem is to hit TAB key several times on login screen or lock screen. After you get focus into the password field again - you will be able to enter password but unable to move cursor using keyboard and unable to login hitting ENTER.
Sometimes it happens without using TAB, as I said.