Apple Remote Desktop: Clients become unavailable if screen locked or curtained during logout
If you use Remote Desktop to take control of a client using Curtain mode, then Log Out on the remote client, the control session will end and you won't be able to take control of the client again unless you force it to restart.
This can also occur if you lock the screen of the client before taking control.
Don't log out on the remote client while controlling it in Curtain mode.
Before logging out, close any windows with sensitive information, end the control session (and Unlock Screen if necessary). Start a new control session in normal (not Curtain) mode and Log Out.