As soon I receive error messages message related to an host Agent I/F as reported below, proxy is not able to get data anymore from Agent (it is detected as available in host configuration but queue related to it does not receive data) until I restart the service on proxy (systemctl restart zabbix-proxy) or I disable the host for a while.

zabbix_proxy.log: 1593:20170922:111800.388 Zabbix agent item "net.if.in[eth0]" on host "pvmas018" failed: another network error, wait for 15 seconds
zabbix_proxy.log: 1593:20170922:111845.396 temporarily disabling Zabbix agent checks on host "pvmas018": host unavailable
zabbix_proxy.log: 1592:20170922:111931.815 enabling Zabbix agent checks on host "pvmas018": host became available
zabbix_proxy.log: 84082:20170922:152227.992 Zabbix agent item "vfs.fs.inode[/u01,pfree]" on host "pvmas018" failed: first network error, wait for 15 seconds
zabbix_proxy.log: 84084:20170922:152242.472 resuming Zabbix agent checks on host "pvmas018": connection restored
zabbix_proxy.log: 84059:20170922:154523.523 Zabbix agent item "net.if.in[eth0]" on host "pvmas018" failed: first network error, wait for 15 seconds