After bridging DXL fabrics in an environment with multiple Trellix ePO - On-prem servers, synchronize certificate authorities (CA) of the TIE servers.
In Trellix ePO - On-prem, select Menu → Automation → Server Tasks, then run TIE Server Synchronize CA.
Verify that the task is completed in the Server Task Log.
If you don't see the TIE server instances, verify that the topology is synchronized.