The easiest explanation I can think of is that you have a file or directory in your site’s directory named “pitch” (such as public_html/pitch or public_html/my-domain/pitch). This can easily be caused by creating the folder for some reason and forgetting about it later or setting up a subdomain such as pitch.my-domain.com which typically will create a directory with the same name as the subdomain.
If this is the cause, your options are:
- Use a different slug (as you’ve already noted).
- Remove or rename the directory. If the directory is connected to a subdomain, you may need to rename the directory to a temporary name, remove the subdomain in your control panel, recreate the subdomain and point it to a directory that doesn’t match the subdomain name (this may or may not be possible with your host), and move all the files from the temporarily renamed directory to the new subdomain directory.
- Create a modification of your .htaccess rewrite rules that causes it to ignore this directory.
Does this sound like it applies in your case?