Why is my server redirecting URLs without a trailing slash to the server's IP address instead of keeping the domain

I’ve set up a droplet for a WordPress site using the provided 1-Click installer. This installs the latest LAMP stack along with Wordpress. I also created a SSL certificate for my site using certbot. I’ve modified my HTTP virtual host file to always perform a redirect to HTTPS.

Everything works as expected except for this one strange behavior. If the trailing slash on the requested URL is not provided by the user, the server performs a 301 redirect to a URL which replaces my domain with the server’s IP address. For example, requesting https://subdomain.domain.com/forum forces a redirect to https://11.22.33.44/forum/. Since my SSL certificate is tied to my domain, it causes a big warning to appear in the browser. I’ve noticed this behavior will always happen regardless of the sub-directory (i.e. will also happen if trying to access http://subdomain.domain.com/wp-includes).

The ONLY exception I’ve noticed with this is when I created a /test directory in the root and created a simple index.html file to display “Hello World”. Trying to access https://subdomain.domain.com/test worked as expected and added the trailing slash without a redirect.

I’ve tried countless things in the .htaccess files without luck. I’m not even confident these files will help. I’ve purposely put a line of garbage in them to see if they’re even active during this redirect and they’re not. The server won’t trigger an error unless I use a URL with a trailing slash. I’ve tried this experiment with the root .htaccess file as well as the one in my /forum directory. However, seeing as how my Hello World experiment was successful (without any .htaccess file), I’m really stumped!

Just for the full background, I already have a fully function site at “domain.com” with a shared hosting provider. I’m experimenting with a migration to DO using this droplet. I’m fiddling around with both sites in my browser, so I’m hoping this isn’t an issue with cookies.