I had faced this problem before.
This issue raised when I installed the "Desktop search" where the application's shortcut is also the same F12.
So I had changed the "Desktop search" shortcut, the quit the application.
then I stopped the running process of yakuake.
Then delete ~/.kde/share/config/yakuakerc.
restart yakuake again, at it worked for me.
I had faced this problem before. share/config/ yakuakerc.
This issue raised when I installed the "Desktop search" where the application's shortcut is also the same F12.
So I had changed the "Desktop search" shortcut, the quit the application.
then I stopped the running process of yakuake.
Then delete ~/.kde/
restart yakuake again, at it worked for me.
Hope this could help.