Which specific setting is unchanged after the save processes? If multiple settings were altered but no settings are being saved, check the browser network activity when you hit the save button. If an unusual redirect is occurring, this may be a server configuration issue.
I have seen similar issues occur when XenForo's base URL is set to http, but the web server has a rule that redirects all http to https. In that case, the web server redirects http to https before a POST can be received by PHP. Usually this kind of issue affects more than just one settings page, or multiple panels in the wiki cp. Are you able to change settings on other setting pages? If not, there is probably a problem with your server configuration.