All Zabbix agents going offline after upgrade Zabbix 4.2 to 5.2

[reicherdotcom]

Hi!

We have a problem with our Zabbix Server which is reporting false positive messages for all agents every day (sometimes multiple times a day).

Here are the server details:
CentOS 8.3.2011 VM (6 CPU cores, 32GB RAM, no swap) with zabbix-server-mysql 5.2.4-1 and MariaDB 10.5.8-1
The Webserver for Zabbix is on another server.

Right after "Zabbix busy housekeeper processes" is going up to 100%, zabbix is reporting the agents offline for about 30 minutes.

In the zabbix-server.log I can find these entries:

1638:20210204:075313.842 slow query: 1276.477113 sec, "insert into history_uint (itemid,clock,ns,value) values
1640:20210204:075313.845 slow query: 1276.482763 sec, "insert into history_uint (itemid,clock,ns,value) values
1636:20210204:080310.057 slow query: 1871.690660 sec, "insert into history_uint (itemid,clock,ns,value) values
1638:20210204:080310.060 slow query: 596.042016 sec, "insert into history_uint (itemid,clock,ns,value) values
1641:20210204:080310.066 slow query: 596.201410 sec, "insert into history_uint (itemid,clock,ns,value) values
1640:20210204:080310.068 slow query: 596.168927 sec, "insert into history_uint (itemid,clock,ns,value) values

This is the mariadb config (server.cnf):

[mysqld]
bind-address=0.0.0.0
innodb_buffer_pool_size = 14336M
join_buffer_size = 512M
key_buffer_size = 1024M
query_cache_type = ON
query_cache_size = 256M
max_connections=1000

This is the Zabbix Server config (zabbix_server.conf):

LogFile=/var/log/zabbix/zabbix_server.log
LogFileSize=0
DebugLevel=3
PidFile=/var/run/zabbix/zabbix_server.pid
SocketDir=/var/run/zabbix
DBHost=localhost
DBName=zabbix
DBUser=zabbix
StartPollers=20
StartPollersUnreachable=20
StartTrappers=10
StartPingers=10
StartVMwareCollectors=1
SNMPTrapperFile=/var/log/snmptrap/snmptrap.log
CacheSize=2048M
StartDBSyncers=4
HistoryCacheSize=256M
HistoryIndexCacheSize=64M
TrendCacheSize=128M
ValueCacheSize=256M
Timeout=20
ExternalScripts=/usr/lib/zabbix/externalscripts
LogSlowQueries=3000
StartProxyPollers=20
StartLLDProcessors=2
StatsAllowedIP=127.0.0.1

Here are some screenshots:



Please let me know, if you need more information.

Thank you for your help.

Best regards,
Ronny