If Keyboard Maestro communicates with the Keyboard Maestro Engine for many facilities. This should never be a problem assuming the Keyboard Maestro Engine is running normally and the system is behaving normally.
So if Keyboard Maestro tells you it cannot communicate with the Keyboard Maestro Engine, something has gone wrong.
First, verify that the Keyboard Maestro Engine is running, which you can do most easily by looking for the Keyboard Maestro icon in the status menu on the right of the menu bar. Select Quit Keyboard Maestro Engine from that menu (at the bottom). Then relaunch Keyboard Maestro Engine by selecting File ➤ Launch Engine from Keyboard Maestro.
If communication is not restored, then there may be a problem with the underlying communicate services provided by the system. The only recourse at this point is to restart.
If you continue to have problems, contact support.