Please check if there’s enough free memory.
You may also check /var/log/elasticsearch/elasticsearch.log to get more information about the error.
EDIT:
I’m working on a nethserver-zammad5 docker version, the current module is bound to version 4 because native install of Zammad 5 isn’t possible anymore, see Zammad ticketing/helpdesk on Nethserver available - #169 by mrmarkuz