Custom menu causes blog page to malfunction

I created a thread related to this issue earlier, but since no one found a solution for me, I spent a few hours troubleshooting the problem myself and am creating this new thread to present my findings. (I hope that didn’t sound rude.)

Here is the blog page in question:
https://thecarolinemedia.com/?page_id=1362

For some reason, it takes the ‘Home’ template instead of the ‘Default’ one, and gives an error message. In the WP dashboard, I checked the blog page to see if it was set to the default template and it is.

The template I’m using is one in which I made alterations to. One of those alterations was making the theme support custom menus because it previously did not.

When I attempted to troubleshoot this, I went to another WordPress site that I have and installed the original version of the template. The blog page worked fine. I then installed my altered version of the template and the blog page worked fine, but the custom menus did not work.

I went back to my thecarolinemedia.com site. I installed the original version of the template and the blog page worked fine. I then set the template back to my altered version of the theme and the blog page did not work. I came to the conclusion that making the theme support custom menus is what’s causing the blog page to malfunction. Can someone help?