The message [No route to host] corresponds to a network host name resolution issue from the OMS host to the target agent's host.
See the following reference for comprehensive network diagnostics for EM components:
Note 428665.1 Enterprise Manager: Installation Requirements and a Checklist for Configuring and Testing Network Connections between EM Component Hosts
1. Ensure the OMS is able to successfully resolve the agent's host name.
2. Ensure that the data returned by the last command is exactly the same as that returned by the other commands, and as shown in the console.
3. Once Agent host name resolution is successful, then proceed with agent resync operation from the console.