Large Amount of Agent unreachable

[unficyp]

Hi,
since our upgrade from Zabbix 3.4.4 to 3.4.6 we experience a large amount of "..Agent unreachable.." waves. Last night we had alone > 400 Mails with unreachable messages coming in from 02:03h to 03:30h.
I was able to check some of the mentioned hosts during the "Mailstorm" with ping/fping and agent.ping - all of the hosts were up and reachable. Checked the switch ports also - no errors on the interface and no bandwith problem.

The only thing we changed was the upgrade to 3.4.6.

Out setup:
Host: Bare Metal Thomas Krenn Server, 4x Xeon E5-2403, 12GB RAM
OS: FreeBSD 11.1 with ZFS Root, 2 (SATA Disks in Mirror :/)
DB: PostgreSQL 9.5.10, Datafiles on ZFS
Zabbix: 3.4.6,compiled from Ports Collection

some changed config options:

StartPollers=25
StartIPMIPollers=4
StartPreprocessors=4
StartPollersUnreachable=10
StartTrappers=4
StartPingers=20
StartDiscoverers=2
StartHTTPPollers=6
StartTimers=5
StartEscalators=4
StartAlerters=6
StartJavaPollers=4
StartVMwareCollectors=10
StartDBSyncers=6
CacheSize=64M
HistoryCacheSize=32M
HistoryIndexCacheSize=8M
TrendCacheSize=16M
ValueCacheSize=128M

Included zabbix internal process busy graph. Checked queuesizes, memory swap, etc.

The only possible problem i see is that the preprocessing process has to much busy % - and the Server specs may be too low.

Aside from that, i don't have a clue where to start looking.

Any thoughts ?
Thanks in advance,
Gerald

[kaspars.mednis]

Please check also Zabbix data gathering processes busy graph, the data gathering processes are responsible for data coillection from hosts

If you run out of pingers or pollers, you are starting to miss data...

Regards,
Kaspars

[unficyp]

The data gathering processes are looking good, none of them above 60%, most of the time they are at 25-40%.

But i think i found the problem - after disabling the housekeeping process, i have no more agent unreachable messages. The Screenshot shows the processes during the "problem". I guess the server/database is a way too slow...

EDIT can't upload the picture, link here: https://ibb.co/kK7vob