Steps to reproduce:

• Followed procedure to enable SSH with Keypair
• Configure Item with SSH Agent 
  

• • No Passphrase on Private Key*

• • File Permission* 

root@zabbix:/home/zabbix/.ssh# ls -lsa id_rsa*
4 rw------ 1 zabbix zabbix 1679 Dec 12 15:12 id_rsa
4 -rwxr-xr-x 1 zabbix zabbix 381 Dec 12 15:12 id_rsa.pub

However I'm having this issue : 

# SUCESS in Root
root@zabbix:/home/zabbix/.ssh# ssh -i id_rsa -p 2222 [email protected]
system/root # 
Connection to 1.1.1.1 closed.

# FAIL in ZAbbix user 
root@zabbix:/home/zabbix/.ssh# sudo -u zabbix ssh -i id_rsa -p 2222 [email protected]
Warning: Identity file id_rsa not accessible: Permission denied.
The authenticity of host '[1.1.1.1]:2222 ([1.1.1.1]:2222)' can't be established.
RSA key fingerprint is SHA256:bCm3+5KuXdqkRMLK31XhBsth1FH+z4oiJOfDMi93FaM.
Are you sure you want to continue connecting (yes/no)? yes
Failed to add the host to the list of known hosts (/home/zabbix/.ssh/known_hosts).
Permission denied (publickey).
root@zabbix:/home/zabbix/.ssh#

however the permission are right. 

Result:

Then got 

became not supported: Cannot access public key file /home/zabbix/.ssh/id_rsa.pub

And 

The permission and ownership of keypair are right however it seem zabbix user didn't have access. 

Question: 

Do you have any hint how can I solve this ?