In the current blogger ( update, many of the users are facing a similar issue which is not showing related posts in their template. 

Follow the steps given below 

1 . Go To Blogger Dashboard , Click On The Theme Option, And After That Click On Edit HTML Option. 

2. After Clicking On Edit HTML You Will See The Template Code. In That Use The Shortcut Key Ctrl + F and Type Related in the Search Box 

3. In Related you will Find A HTML Code with Condition 

Note: In Themes You Will Find 2 Similar Conditions Shown In Screenshot, You Have To Delete Both The Conditions. 

4. Delete the the Condition Shown In The Point Number 3 And Save It your related Post will Start working After That. 

 Result :