There are often 2 common situations that users can encounter the “404 Page not found” error

• After activating the theme
• After publishing a new page

To solve the error occurred in the first situation:

In WP admin panel, navigate to Settings > Permalinks and click Save Changes. This will update the “.htaccess” file to work with custom post types correctly.

To solve the error occurred in the second situation:

In WP admin panel, navigate to Settings > Permalinks > Common Setting tab, choose Post Name and click Save Changes