Active Agent communicating, but no data showing on server

[coretechs]

Hi everyone, hoping someone can assist.

We have Zabbix server on ver 5.0.5 (ubuntu) and I have another remove ubuntu server with latest zabbix agent installed and configured. We've done this numerous times without issue, but are experiencing issues now.

zabbix agent installed and configured with:

• Passive and active server hosts set to the remote server
• ports on remote server opened and telnet communication verified from the agent server
• config hostname configured
• psk settings configured in the conf file and working
• Server is configured for Autoregistration.

Agent is installed and starts up. It auto-registers itself successfully with the server so the server 100% has the correct hostname. We can also see psk settings etc and they're all correct.

We've applied the default linux template to the host

doing a tail on the agent conf file gives:
IPv6 support: YES
20083:20210528:032143.479 TLS support: YES
20083:20210528:032143.479 **************************
20083:20210528:032143.479 using configuration file: /etc/zabbix/zabbix_agentd.conf
20083:20210528:032143.487 agent #0 started [main process]
20087:20210528:032143.489 agent #2 started[listener #1]
20088:20210528:032143.490 agent #3 started[listener #2]
20089:20210528:032143.494 agent #4 started[listener #3]
20090:20210528:032143.498 agent #5 started [active checks #1]
20086:20210528:032143.500 agent #1 started [collector]

Server show host with a red ZBX. This is usually grey as they're remote active agents. Error on server is "get value from agent failed. Cannot connect too ... [4] interrupt system call".

Clearly there's communication seeing the agent registers itself, and clearly the settings are correct for all this too happen. We even copied the conf file from a working server/agent that's almost identical, changed the hostname etc. Same deal.

Any thoughts? cheers