I just installed elementary OS on a iMac (27-inch, Mid 2011), with AMD Radeon HD 6770M. It generally works well, except one thing:
When I lock the screen super + L, or leave the screen and then come back and the screen is off and locked.
When I unlock everything is unresponsive, or at least very slow.
When I press a button it takes several seconds before I react.
Sometimes I can just go standby, and back and everything is back to normal. Sometimes I have to reboot to solve the problem.
Have you tried restarting lightdm?? When you get you screen locked, press CTRL + ALT + F1 and you will enter in console mode, then log in and execute the next command.
sudo service lightdm restart
if nothing happend then press again CTRL + ALT + F1 and check for an error message
Do you have any idea for permanent solution for this issue? Because restart of lightdm means closing all programsand that the system becomes unusable...
lightdm you can CTRL + ALT + F1 then login to user type killall light-locker then switch back CTRL + ALT + F7 (and start light-locker & again in terminal.