I just updated to the latest version of Little Snitch.
After reboot, I typed my password and it got stuck where you see all the "balls" for each letter in the password, on the login page. Frozen up, no mouse, nothing at all - only holding down the power button to restart. But it happened again at each login. One time, it got stuck at the Apple Logo. There was no startup sound.
I did a SMC reset and PRAM reset, and after that I am back to normal.
(look up pram reset in your favourite search engine for details)
This is just in case others have the same problem.
I am a long time Little Snitch user, but only registered on the forums here today, to share this with others.