I have a linux (18.04 LTS) running the zabbix-agent2 5.0.19, whenever I run it  in the foreground, i get the correct result back on our zabbix-proxy by testing with:

–
/bin/zabbix_get -s IP.IP.IP.IP -p 10050 -k "proc.num[apache2]" 
0
while requesting the systemtime for example, that appeats to be working.

–

When running  (with the agent running as daemon) the monitored machine itself, we get the following:

/usr/sbin/zabbix_agent2 -t proc.num[apache2] -v
proc.num[apache2]                             [s|11] 

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When we do the same with the zabbix-agent2 running in the foreground on the monitored server, i get the following result on the monitoring proxy:

/bin/zabbix_get -s IP.IP.IP.IP -p 10050 -k "proc.num[apache2]"
11

-

The only difference I see between both situations is that, when running in the foreground it runs as root, while running it on the background it uses the zabbix users...