how you're updating the clients by using a task or manual update.
please check the windows firewall status and also try to update manually.
I am updating the clients by using a task and manual update.The windows firewall status also disabled。
What version of the Agent and ePO do you have? Are there any recent changes you've done to either? This does sound like a firewall blocking communication because you can get policy and task but not wake up calls. Will the agent check in once it's hit its mandatory check in time?