After I upgraded from 3.2.5 to 3.4.3 I have the problem that the agent ping remains on error, although this is UP again.
Workaround restart zabbix server or stop zabbix agent and start agent after approx 10 minutes. If I use the agent option then I have the agent-Ping error twice Screenshot_4. Is the agent ping up again both enties schow OK.
I usually have this problem with WAN. For 10 devices, 8 show OK in case of a failure. 2 remain on error.