I have this a template that has this code:
<h3 class="futura">General Info</h3>
{exp:channel:entries channel="online_courses" orderby="nav_order" sort="asc" dynamic="no"}
{sp_left_nav}
{if item == 'Display on Online Classroom Main'}
<a href="{title_permalink='online_courses/general'}">{title}</a>
{/if}
{/sp_left_nav}
{/exp:channel:entries}
<h3 class="futura">Courses</h3>
{exp:channel:entries channel="courses" orderby="nav_order" sort="asc" dynamic="no"}
{sp_left_nav}
{if item == 'Display on Online Classroom Main'}
<a href="{title_permalink='online_courses'}">{title}</a>
{/if}
{/sp_left_nav}
{/exp:channel:entries}
I have a checkbox custom field called sp_left_nav. The entry that I'm viewing has the checkbox for "Display on Online Classroom Main" checked.
This is how it shows when presented.

As far as we know, this has only begun happening today as we haven't changed this template since 2014.
One of my content editors made a change to an entry in the courses channel that has the checkbox "Display on Online Classroom Main" checked.
Now, we have a staging site and it has the exact same code and content and it doesn't show the same.
Any ideas???