After the message is published one of the receiving clients has to acknowledge the reception and afterward has to confirm that the server may clear the information. This mechanism is usually used to call for human assistance. The client PLC acknowledges the reception and shows a message on its HMI. After the operator gives the command to continue the PLC sends the confirmation to inform the server.
If the vision System has its own user console such a user confirmation may be entered there. Therefor it is allowed that the vision system may clear the message even without the confirmation received from a client. But it has to wait for the reception of an acknowledgement before doing so.