Troubleshoot Ajax issues on preexisting website

I have a preexisting social media website that uses Ajax for synchronous alerts in the top navigation bar, telling members that they have received messages, a friend request, or a new forum comments was added in the recent activity sidebar. Lately, it's not working. I suspect recent tweaks have broken this functionality and I'd like to fix it.

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Please note: THIS IS AN ADULT SITE. Please DO NOT bid on this site if working on adult sites is something you prefer to avoid. Additionally, please be experienced in PHP and the Wordpress CMS. Fluent English desired. No agencies, please: I prefer to work with talented individuals.