The the zabbix-agent get the wrong memory values in a Linux Container which is limited with cgroup.
It seems that the zabbix-agent report the memory values of the host system and not from the container. So it is useless for triggers.
top in the container shows the correct values.
also /proc/meminfo shows the correct values.

A Simple workaround is to detect if you are in a lcx-container (/proc/1/environ) and do not use this values in the trigger.