Page Title changing to "undefined" when using AJAX links

Hi there. I am running a custom theme based on the Bootstrap development framework. Here is the code I am using in my theme’s header.php file to set the page title:

<title>
		<? wp_title( '|', true, 'right' ); ?>
		<? bloginfo('blogtitle'); ?>
		<? $site_description = get_bloginfo( 'description', 'display' );
		if ( is_front_page() ) { echo ' | '.$site_description; } ?>
	</title>

This plugin is working perfectly for me except for one thing. When using any links that load content with AJAX, the page title is getting set to ‘undefined’.

So for example, if I load

https://www.mysite.com/events
the page title is set to
Upcoming Events | My Site

If I click on the navigation links at the bottom, the page title changes to
undefined

If I reload that page
https://www.mysite.com/events/past
the page title is set to
Past Events | My Site

If I click on the title of an Event from any of the lists, the page title is
Name of Event | My Site

but if I click the Back button to return to the list, again the page title gets set to
undefined

I have tested this on a different install using the default WP theme and this issue doesn’t happen in that case. My question is, could it be possible for the Bootstrap jQuery code to be interfering with this plugin in some way? If there are other known plugin conflicts, could someone point me in the right direction to see if I am running any of those plugins? Any suggestions at all for where the bug in my theme could be?

https://www.ads-software.com/plugins/the-events-calendar/