As the CCM had a problem this morning and I wasn't able to solve it by doing a process state restart or monitoring engine restart, I decided to reboot the server and I have the same problem as the last time I rebooted the server. All my hosts are in grey state and notifications are disabled.
Just had to expand the disk and add two cores to the Nagios XI server and after the reboot all hosts were greyed out again. Applying configurationn helped, but as I already deleted the retention.dat file not long ago, What could be the reason my hosts are going grey after a reboot? I saw this problemn the last 4 reboots I've done to the server.
Looks like you may not be retaining status information on your objects, to change this, navigate to them in the CCM and under 'Check Settings' make sure that Retain Status Information is ticked, then save and apply configuration on them.
I'm sorry Sam, but all the hosts I have and these are multiple types of hosts ranging from switches, servers, web applications, who are all greyed out after a reboot. The template's retain status information is on, so I still have no idea why all my hosts are greyed out after a reboot.