The error "CE_AGENT_OFFLINE" appears if the Agent goes offline (disconnects from Management Console) when it has an active job run.
The error indicates that the Resilio Connect Agent is not actively connected to the Management Console. It does not necessarily mean it is unable to establish a connection with other Agents in the Job, but in most cases it actually is.
To verify it go to job run, click on any of the agents that are supposed to be connected to the offline Agent, and check the connection status on the Connectivity tab.
If the agents are disconnected from each other, that will impact job completion. Check that the agent process still runs on the server. Refer to this article to verify that the network tunnel is available between Agents.
You can assign a notification for the "CE_AGENT_OFFLINE" error and set it to notify you via an e-mail only if the error is not resolved. Below is an example for setting this value to 2 days:
Error code CE_AGENT_OFFLINE