Unable to switch users at lock screen. Unity, Ubuntu 18.04

If I am logged in as a user or at the lock screen, I am unable to switch accounts to another user. When I click on the symbol in the top right and click on the name of another user to switch to, nothing happens.

It's ok if I'm logged in because I can just log out, but that's not an option at the lock screen. The only way to switch to another user is to restart the computer which is annoying. I'm using Unity with lightdm on Ubuntu 18.04.

Anyone else have this issue? Or have an idea how to fix it? Thanks!

I was able to fix it by removing lightdm, re-installing lightdm, and then rebooting. Not sure what went wrong, but I can switch users again no problem.

sudo apt-get remove lightdm
sudo apt-get install lightdm