But when i go to appearance – customize i see the related post. but when i close the customizer the related post gone.
You will indeed always see Related Posts in the customizer, as a preview of how it could look on your site. The Related Posts displayed there are examples.
On your posts, however, we try to pull real Related Posts. That does not quite work on your site, because when querying for Related Posts we get the original post back instead:
https://kabar-aneh.com/misteri/domba-aneh-warga-afrika-panik/?relatedposts=1
Compare this with what we should normally get on a site using Related Posts:
https://jeremy.hu/jetpack-remove-the-share-counts-from-the-sharing-buttons/?relatedposts=1
Do you use a caching plugin that may cache pages with a query parameter? If so, could you check your caching plugin options to avoid doing that, thus returning related posts for those queries?
If you do not use such a plugin, I would recommend that you get in touch with your hosting provider and ask them if they have a caching layer in place on your site, such as Varnish, that could return cached pages.
I hope this helps.