Restarted zabbix-server service 2 times but it not work
Rebooted zabbix server and RDS server
disabled all the hosts, around more than 800
started enabling few hosts, till 350 everything was working fine. But suddenly after adding other 100 hosts we started seeing the same errors.
All the hosts were seen out of sync with the zabbix server.
restarted the zabbix server.

As off now on hosts are stable.