Hello Sheldon ,

Sorry for late reply to this,
The reason the related blog post module doesn't show in your site is because the module will only appear on your blog entry page and which blog post have the same tag with another blog post.

Try check my test blog post here -> http://demo.impression-estudio.gr/acf/letters-from/entry/test.html
I have insert the Japan and Asean tag in that test post, then the module will appear. Please have a check.