Error 404 in templates

Have you ever experienced your template editor showing a 404 error page instead of builder elements, like in the screenshot?:

It is a problem with WordPress and is present in the custom post types (like templates). The root cause of it is the so-called Rewrite Rules.

Rewrite rules are how WordPress creates clean/pretty URIs from URL query parameters. When your new page or blog post automatically gets a human-friendly URL, this is provided by a rewrite rule, which uses WordPress's Rewrite API.

When installing Betheme or any other theme or a plugin that creates a custom post type with its own "rewrite_rule" address rewrite method, we need to refresh all methods stored in WordPress. Without refreshing, the new method will not load, and when entering a post with a new custom post_type, a 404 error will be shown. If you have noticed this problem, you can solve it by saving the permalinks again. All you have to do is go to Wordpress Dashboard Settings -> Permalinks and click the save changes button. U don't need to do anything more than that. After, you shouldn't experience the 404 error any more.