Ok,
So you have changed your vCenter,
So please try this :
1 - Put the Host in maintenance Mode
2 - Remove the server
3- Add the host again
If that does not work try.
Run the following command as root in the console of each of the hosts.
/opt/vmware/aam/bin/VMware-aam-ha-uninstall.sh and reconfigure the HA agent.
Regards,
Julien