What is the process you are following to deploy the HA cluster? What is the network topology - active/passive link? Asymmetrical?
Have you identified what is the device experiencing the issue? You should be able to check the switch/router logs to see if there is any protocol impacted when you put the failover device inline
If you can provide all the details for the process you are following, then we should be able to figure out what's going wrong and why