It’s nothing new that Elasticsearch by default takes 50 percent of your memory.
Search for “heap size” in the elasticsearch documentation and limit the memory usage to something like 2GB.
Don’t know what the other problems are, but most likely they can be fixed with slight performance tuning ( Configuration via Environment Variables — Zammad System Documentation documentation ) and ensuring you’ve configured the system to expactations ( Configure Database server — Zammad System Documentation documentation )