If you experience the Problem that your Checkmk core (cmc) is killed by a SIGKILL from the Kernel, It is worth a try to check if the ULIMIT is set right.
Check it with:
ulimit -a
Check in your /etc/security/ folder for a limits.conf or limits.d folder.
There you can add:
username soft nofile 65535
username hard nofile 65535
replace username with the sitename and restart omd.