It seems that the post is getting refetched over federation and marked as deleted again. So you will have to run that SQL query regularly (eg in a cronjob) to restore the post every time. Its also worth setting locked = true to prevent users from commenting.

By the way I opened an issue to fix this properly: https://github.com/LemmyNet/lemmy/issues/6044

You can run the SQL command update post where id = 53505862 set deleted = false. That way it will be visible on db0 again, although not on other instances.