Now that your timezone settings were resolved in your last post, does doing a Delete (Tools > Write Config Files) and then Apply Configuration resolve the issue?
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It could also be a permission issue. Try the following.
Configuration Applies, No Changes Take Place
This is generally due to permissions issues with the configuration file. Use the Write Config Tool in the Core Config Manager to see if you can manually write the DB information to the config files. If the Write Config Tool returns error messages related to permissions you can run the following script to correct the permission settings:
/usr/local/nagiosxi/scripts/reset_config_perms
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