Host availability is 'gray' for agent [FOR HELP]

Host availability is 'gray' for agent  [FOR HELP]

I have added about 40 freeBSD servers as hosts. Each server has the agent installed. Most of them come up as a green Z icon in the Zabbix hosts list. The rest are all red.



When I delete the host ,and then add again the same host，the availablility became “gray” ，why ???



The zabbix_agent（119.254.72.159） is running normally


And the server IP（119.254.72.250） of the agent configuration file is right


In addtion,the server（119.254.72.250） can get data from the agent（119.254.72.159）


I don't know how to get them all green. I've done them the same as the first one, which is green.


Any ideas?
Thankyou a lot