Zabbix 3.0.11 - Server is not running, Unable to display Queue, Trapper 100% busy

[Peteris]

Hello,

We upgraded to Zabbix 3.0.11 on Monday and last night something went wrong.

Server displays "Zabbix server is not running" intermittently. Same if you refresh main page 50% at the time it will say Zabbix server is not running, then refresh and it will display that server is running.

From what I can tell all the information is being collected without issues, so the server is not actually failing and coming up all the time.

Trapper process has gone from 0% to 100% busy ~ 4AM this morning and rebooting server didn't resolve the issue. Adding more trapper processes didn't help either. Server has enough performance and we are not using active check at all.

And most bizzare issue is that Web Front End wouldn't display Queue at all, we get two type of errors:

#1 Error

Cannot display item queue.
Details
Connection to Zabbix server "HOSTNAME" timed out. Possible reasons:
1. Incorrect server IP/DNS in the "zabbix.conf.php";
2. Firewall is blocking TCP connection.
Connection timed out

#2 Error

Cannot display item queue.
Details
Connection timeout of 3 seconds exceeded when connecting to Zabbix server "HOSTNAME".

I can see that Queue information from Monitoring->Latest Data on Zabbix Server displays Queue = 0, but the actual Administration->Queue page wouldn't display.

I have tried increasing amount of trappers, DB syncers, DB allowed connection amount, and even ZBX_SOCKET_TIMEOUT from 3 seconds to 30 and it doesn't help.

Any suggestions? Seems like a bug.

[Peteris]

OS: CentOS Linux release 7.4.1708 (Core)
MySQL: mysql Ver 14.14 Distrib 5.7.19, for Linux (x86_64)