Considering you are able to apply configs and are not getting errors. The most likely issues are either time zones\time is not set correctly, or file permissions issues.
Time Zones
Go to Admin->System Config and look for Date/Time and verify that PHP and System Time are the same, as well as that the timezone is correct.
File Permissions
Provided time is set correctly, it is most likely an issue of writing to the file that contains these two services. The nagios user needs to be able to write to them, for the sync to complete correctly.
Nagios-Plugins maintainer exclusively, unless you have other C language bugs with open-source nagios projects, then I am happy to help! Please pm or use other communication to alert me to issues as I no longer track the forum.